A text-book of hygiene : a comprehensive treatise on the principles and practice of preventive medicine from an American standpoint

Preface

The aim of the author in writing this book has been to place in the hands of the American student, practitioner, and sanitary officer, a trustworthy guide to the principles and practice of preventive medicine.

He has endeavored to gather within its covers the essential facts upon which the art of preserving health is based, and to present these to the reader in clear and easily understood language.

The author cannot natter himself that much in the volume is new. He hopes nothing in it is untrue.

CHAPTER I.-Air

The composition and physical conditions of the atmosphere, 2-6. Influence of changes of atmospheric pressure on health, 6-9. Influence of changes of temperature on health, 9-10. Humidity of the atmosphere as connected with changes in health, 10-12. The sanitary relations of changes in composition, and of impurities in the air, 12-17. Sewer air, 17-19. Tests for impurities in the air, 19-22. Ventilation, 22-28.

CHAPTER II.— Water, 29-57

Quantity of water required by human beings, 29-31. Sources of drinking water, precipiiation, rivers, lakes and ponds, springs, wells, distillation, 31-39. Qualities of good drinking water, 39-40. Impurities in water, 40-42 Diseases due to impure drinking water, 42-51. Storage and purification of water, 51-53. Tests for impurities in water, 53-55. Signification of various impurities in water, 55-57.

CHAPTER in.— Food, 58-87.

Quantity and character of food necessary, 58-62. Foods, 62-63. Foods of animal origin, 63-73. Foods of vegetable origin, 73-76. Cooking, 76-79. Beverages containing alcohol, 79-84. The alkaloidal beverages, 84-86. Tobacco, 86-87.

CHAPTER IV.-Soil, 88-102

Physical and chemical characters of the soil, 88-89. The atmosphere of the soil, or ground-air, 89-94. The water of the soil, or ground-water, 94-96. Diseases spread by soil impurities, 96-99. Diseases of animals due to soil impurities, 99-101. Drainage, 101-102.

CHAPTER V.— Removal op Sewage, 103-119

Quantity of sewage to be removed, 103-104. The privy and privy-well systems, 104- 107. The Rochdale, or pail-closet system, 1P7-110. Earth and ash closets, 110-111. The pneumatic system of Liernur, 111-113. The water-carriage system, 113-117. Final disposal of sewage, 118-119.

CHAPTER VI.— Construction op Habitations, 120-141

Influence of insanitary dwellings upon health and life, 120-122. Site, 122. Character of soil, 122-127. Materials for construction of dwellings, 127-129. Size of rooms, and ventilating and heating arrangements, 129-130, Internal wall coating, 130. Lighting, 130-132. Water-supply, 133. House drainage, 133-134. Water-closets, 134-137. Water-supply for closets, 137. Traps, 137-138. The soil-pipe, 138-139. The house-drain, 139- 140. Official supervision of the sanitary arrangements of dwellings, 140-141.

CHAPTER VII.— Construction op Hospitals, 142-153

Site, 142. The buildings, 142-145. Ventilation and heating, 115-147. Interior arrangements, 148-150. Administration and management of a general hospital, 151-153.

CHAPTER VIII.— Schools, 154-164

Construction of school-houses, 154-157. School furniture, 157-158. Amount of time to be devoted to study, 168-159. Diseases of school-children, 160-164.

Till TABLE OF CONTENTS.

CHAPTER IX.— Industrial Hygiene, ; 165-189

Relation of occupations to health and life, 165-168. Occupations prejudicial to health, 168. Diseases due to the inhalation of irritating or poisonous gases or vapors, 169-179. Diseases due to the inhalation of irritating or poisonous dust, 179-183. Dis • eases due to the absorption or local action of irritating or poisonous substances, 183- 186. Diseases due to the excessive use of certain organs, 187-188. Diseases due to a constrained attitude and sedentary life, 188. Diseases from exposure to mechanical violence, 188-189.

CHAPTER XIX.— History of Epidemic Diseases, 243-297

The oriental plague, 243-24S. The sweating sickness. 248-250. Small-pox, 250-266. Asiatic cholera, 866-376. Relapsing fever. 877-878. Typhoid fever, 278-280. Typhus fever, 2S0-281. Yellow fever, 281-2S4. Scarlet fever and measles, 884-385. Diphtheria, 285-287. Dengue, 2S7-288. Epidemic influenza, 28S-2S9. Epidemic cerebro-spinal meningitis, 289-291. Syphilis, 291-294. Diseases of animals communicable to man;. sheep-pock, actinomycosis, bovine tuberculosis, rabies, anthrax, glanders, 291-297.

CHAPTER XX.- Antiseptics and Disinfectants, 29S-303

Comparison of antiseptics and disinfectants, 896-899. Relative germicidal power of different agents, 299. Resistance offered to the action of disinfectants bv different organisms, 301. Methods of disinfection. 306. Antiseptic*. 308.

TABLE OF CONTENTS. IX

CHAPTER XXI.— Quarantine, 80M08

Objects of quarantine, 304-305. Modern notion of quarantine. 805-308,

CHAPTER XXH.-Vital Statistics, 309-314.

Registration of deaths, 309-310. Registration of births, 310. Registration of mar riages, 311. Registration of diseases, 311. Death-rate and birth-rate, 312-314.

ComtECTioN :— On page 169, 'sulphuric acid gas' should read sulphurous acid yas.

TEXT-BOOK OF HYGIENE.

Chapter I. A I R

Exact investigation into the influence of the atmosphere npon health is yet in its infancy. Enough has been learned, however, to show that changes in the composition of the air, in its density, its temperature, its humidity, its rate and direction of motion, and possibly its electrical or magnetic conditions, influence in various ways the health of the individual. It is only very recently that any scientific attempts have been made to trace the bearing of atmospheric changes upon health. The observations already recorded indicate that a thorough study of meteorological phenomena in connexion with the origin and progress of certain diseases, is a promising field of labor for the educated sanitarian. The meteorological observations which have been gathered by the United States Signal Service during the past thirteen years, already form such a large and tolerably complete and well-arranged body of facts, that reasonably accurate deductions can even now be made. Heretofore, in studying the sanitary relations of the atmosphere, both in this country and abroad, the attention of observers has been riveted almost exclusively upon the changes in its composition occurring within certain limited areas. It is, perhaps, equally important to study this universally diffused and necessary condition of vital activity in its broader and more general relations. It will be shown in the course of the present work, that the meteorological features of countries, or of seasons, or even the daily atmospheric changes, exercise an important influence a TEXT-BOOK OF HYGIENE.

upon life and health. In order to fully appreciate these relations it will be necessary to first give a brief summary of the facts and laws of meteorology.

THE COMPOSITION AND PHYSICAL CONDITIONS OF THE ATMOSPHERE.

Atmospheric air is a mixture of four-fifths of nitrogen and one-fifth of oxygen ; more accurately 79.00 of the former, to 20.96 of the latter. In addition, there is constantly present a modicum of carbonic acid, usually about .04 per cent., (3 to 5 parts in 10,000), and a variable proportion of vapor of water.

These proportions are maintained, with very little change, at different heights. At first thought, it would seem that carbonic acid, being much heavier than the other constituents of air, would accumulate in the lower regions of the atmosphere, but in obedience to the law of diffusion, the intermingling of the component gases is perfect, and the proportion of carbonic acid in the atmosphere is quite as great on mountaintops as in the deepest valleys.

The proportion of nitrogen in atmospheric air is generally uniform, while that of oxygen varies, depending to a great extent upon the amount of carbonic acid present. Hence an increase in the amount of the latter constituent is usually accompanied by a diminution of oxygen, inasmuch as the formation of carbonic acid can only take place at the expense of oxygen. The reciprocal activities of animal and vegetable life are beautifully illustrated by these relations between the oxygen and carbonic acid in the air. In the processes of combustion and oxidation, oxygen is" withdrawn from the atmosphere and combines with carbon, forming carbonic acid. During vegetable growth, on the other hand, carbonic acid is withdrawn from the air by the leaves of plants, and decomposed into its elements, carbon and oxygen. The carbon is used in building up the plant, while the liberated oxygen is restored to the atmosphere. The animal consumes oxygen and gives out carbonic acid ; the plant resolves this compound into its constituent elements and gives back the oxygen to the air again.

The atmosphere extends upward from the surface of the earth to an indefinite distance. The limit has been variously placed at from forty-five miles to twenty-five thousand miles. In obedience to the law of gravity, this mass of air everywhere presses directly downward — toward the earth' s centre — with a force equal to its weight. If a column of this air be balanced by a column, or mass of any other matter — the columns being of the same diameter — we have a relative measure of the weight of the atmosphere. The instrument with which the weight, or downward pressure of the air is measured, is called a barometer. The atmosphere, at the sea-level, presses downward with a force equal to the pressure of a column of mercury thirty inches high. Hence, the barometric pressure at sea-level is said to be thirty inches. If the barometer be carried to the summit of a mountain one thousand feet above the level of the sea, or taken to the same altitude in a balloon, the mercury in the barometer tube will fall about one inch. This inch of the mercurial column represents the weight of the one thousand feet of air now below the barometer, and consequently not measured or balanced by it.*

Upon ascending from the sea-level, it is found also that the air, being less pressed upon by that which is still above it, becomes more rarefied and lighter ; its tension, as it is termed, is less. Hence, for the second thousand feet of ascent above the sea, the mercury will

* The figures here given are not absolute, but merely approximate. The limits of this work do not allow a full discussion of the meteorological elements modifying the pressure of the atmosphere at sea-level.

fall a less distance in the tube, the weight removed not being so great as in the first thousand feet.

Variations in temperature and humidity of the air influence the tension of the atmosphere in a marked degree, and affect the height of the barometric column. In fact, most of the changes of atmospheric pressure at the surface of the earth, are directly due to changes in temperature and humidity. Increase of temperature diminishes the density of the air. Hence, when the temperature rises, the pressure decreases. The proportion of moisture (aqueous vapor), if increased, likewise causes a diminution in pressure.

The warmth of the air is primarily derived from the sun. On a clear day about one-fourth of the heat of the sun's rays is given off directly to the air during the passage of the heat-rays to the earth. Of the remaining three fourths, part is reflected from the earth, while the larger portion is first absorbed by the earth and then given off by radiation and convection to the superincumbent air.

The air is always warmer near the earth' s surface on a clear, sun-shiny day ; for, as soon as the earth gets warmer than the air immediately above it, the excess of heat is given off to the latter by convection and radiation. On ascending from the surface of the earth the temperature decreases, and on the summit of a high mountain, the air is always colder than at its base.

Prof. Tyndall has shown that dry air does not absorb heat. For this reason, the sun's rays strike the earth with much greater intensity on a very dry than on a moist day, while on the latter a larger proportion of the heat rays is intercepted before they reach the earth.

Air at different temperatures is capable of absorbing different amounts of aqueous vapor. Thus, air at a temperature of 40° will require a much smaller amount of vapor to produce saturation than air at a temperature of 80°. For this reason air which appears 'damp' at the former temperature, both to the bodily sensations and to appropriate instruments, would be considered as 'dry' at the latter temperature, although the actual amount of vapor present, or absolute humidity, is the same in both cases.* In meteorological observations for sanitary purposes, the relative humidity is the condition deserving especially careful study.

The motion of the air — wind — is caused by differences in pressure ; the latter being due to differences in temperature and humidity. A mass of air traversing a large body of water absorbs vapor, unless already saturated, and becomes moist ; if it passes over a wide tract of dry land it loses moisture and becomes dry. Therefore in the eastern portion of the American continent, an easterly or southerly wind which comes from over large bodies of water, and which is usually warm, and thus capable of holding a large quantity of water in a state of vapor, is always moist. On the other hand, a northerly or westerly wind, coming over a large extent of dry land and from a colder region, is nearly always a dry wind. On the Pacific coast these conditions are reversed ; there a westerly wind is a moist wind, while an easterly wind is dry. It is probable that the direction and rate of motion of air- currents have considerable influence upon the origin or intensification of certain diseases.

The electrical and magnetic conditions of the atmosphere have been as yet studied to little advantage. It is only known that atmospheric electricity is in most cases positive, and that its intensity increases

* By 'absolute humidity' is meant the total amount of vapor present in a certain mass of air. By the term 'relative humidity' meteorologists designate the proportion of vapor present at certain temperatures, compared with full saturation of the air with vapor, which is reckoned 100. Thus, air which is saturated, or whose relative humidity is 100 at 40°, would have a relative humidity of only 24, if the temperature were raised to 80°, because in the latter case the capacity of the air for aqueous vapor is increased. Relative humidity is always designated in percentages ; absolute humidity in grains per cubic foot.

with condensation of vapor. There seems to be no doubt that the varying states of atmospheric electricityare closely connected with evaporation and condensation. There is reason to believe that a fuller knowledge on these topics will yield most important results to the student of hygiene.

The presence of ozone in the atmosphere has a very decided interest to the sanitarian. This modified form of oxygen which was discovered by Schcenbein in 1839, is formed wherever there is oxidation without a very high temperature. * What functions ozone performs in the air except as an oxidizing agent, is not known. An impression prevails largely that it has an important bearing upon the causation of disease, but too little is known upon the subject to form the basis of a rational theory.

The presence of ozone is detected by test paper, the best being Schcenbein' s, prepared as follows : Add ten parts of starch to two hundred parts of pure water ; heat it until the starch gelatinizes, and then dissolve one part of potassium iodide in the mixture. This paste is then spread on unsized paper and rapidly dried without exposure to sunlight. The paper is then kept in a dry, dark place, until wanted for use.f

INFLUENCE OF CHANGES OF ATMOSPHERIC PRESSURE ON HEALTH.

The effects of a considerable diminution of pressure are familiar to every one in the 'mountain sickness' which attacks most persons on ascending high mountains. M. Bert has shown experimentally that similar effects can be produced in an air-tight chamber by diminishing the pressure.:}: The symptoms produced under a

* R. C. Kedzie : On Ozone. Third Annual Report of the Michigan State Board of Health, I8T5, p. 137.— On Ozone and Atmospheric Electricity, see an instructive paper by the late Dr. George M. Beard, in Popular Science Monthly, Vol. IV., p, 450.

t See Kedzie, above Quoted, p. 143.

pressure equivalent to an altitude of from 13,448 feet, to 16,728 feet, were a feeling of heaviness, nausea, ocular fatigue, rapidity of pulse and convulsive trembling on slight exertion, and a sensation of languor and general indifference to the surroundings of the individual. M. Lortet, who has left on record his experiences in the higher Alps, says that the symptoms noticed on ascending to high altitudes are labored respiration, increased rapidity of pulse, depression of temperature, (as much as 4°-7° C). The normal temperature was restored, however, after a brief rest. * Still more severe symptoms have been noticed on ascending high mountains in South America and Asia. Aeronauts have lost consciousness, and in several instances life, on rapidly ascending to great altitudes, f According to the observations of the brothers Schlagintweit, distinguished explorers of the highlands of Asia, the effects of diminished pressure upon the human organism are : ' headache, difficulty of respiration, and affections of the lungs,— the latter even proceeding so far as to occasion blood-spitting, want of appetite and even nausea, muscular weakness, and a general depression and lowness of spirits. All these symptoms, however, disappear in a healthy man almost simultaneously with his return to lower regions.' A singular observation was made by these travelers on the effect of motion of the air upon the symptoms described. They say : ' The effects here mentioned were not sensibly increased by cold, but the wind had a most decided influence for the worse upon the feelings. . . . When occupied with observations, we took very little, if any bodily exercise, sometimes for thirty- six hours ; it would frequently occur nevertheless, even in heights not reaching 17,000 feet, that an afternoon or evening wind would make us

* Real-Encyclop£edie d. ges. Heilk. V., p. 529.

t MM. Sivel and Croce-Spinelli, two asronauts, lost their lives in this manner during an ascent from Paris, in April, 1875.

all so sick as to take away every inclination for food. No dinner was cooked; the next morning when the wind had subsided, the appetite was better.

'The effects of diminished pressure are considerably aggravated by fatigue. It is surprising to what degree it is possible for exhaustion to supervene ; even the act of speaking is felt to be a labor, and one gets as careless of comfort as of danger. Many a time our people, — those who ought to have served us as guides — would throw themselves down upon the snow, declaring they would rather die upon the spot than proceed a step further.'*

These symptoms disappear when persons are exposed to these conditions for a prolonged time. Thus, in the Andes there are places thirteen and fourteen thousand feet above sea-level, which are permanently inhabited ; and in the Himalayas there are villages at a height of over 15,000 feet constantly occupied. In this country, Pike's Peak, 14,150 feet above the sea, has been occupied since 1873 by observers of the signal service. The men seem to become acclimated, as it were, and suffer little or no inconvenience f rbm the diminished pressure, after a time.

The effects of increased pressure of the atmosphere are especially manifested in divers, and in workmen in deep mines and tunnels. The symptoms are decrease of respiration, diminution in frequency of the pulse, ringing in the ears, earache, headache, mental depression and sometimes actual deafness. 'When the workmen leave the compressed air, they are said to suffer from hemorrhages and occasional nervous affections, which may be from cerebral or spinal hemorrhages, 'f The workmen, however, soon become habituated to these

* Results of a Scientific Mission to India and High Asia. By Hikmaxx, Adolphe and Robert De Schlagintweit. Vol. n., pp. 484-5.

t Pakkes' Practical Hygiene, 6th ed., New York. Vol. H., p. 92.

changes and then suffer little inconvenience upon exposure to the increased pressure.

INFLUENCE OF CHANGES OF TEMPERATURE ON HEALTH.

Many of the derangements of health ascribed to high temperature are to a considerable degree due to other factors, prominent among which are high humidity, intemperance, overwork and overcrowding. There can be little doubt, however, that the importance of the high temperature itself can hardly be overrated. It has been generally accepted heretofore that a high temperature together with a high relative humidity is most likely to be followed by sunstroke. A careful comparison in a series of deaths from sunstroke in the city of Cincinnati in the summer of 1881, shows, however, conclusively, that a very high mean temperature with a low relative humidity is more liable to be followed by sunstroke than the high temperature when accompanied by a high humidity. The same series of observations also shows that the number of deaths was greater on clear days than on cloudy or partly cloudy days.* A corroboration of this result is found in the fact that sunstrokes very rarely occur on shipboard, at sea, where the relative humidity is always high.

Diarrhceal diseases, both of adults and children, are much more frequent during hot than during cold weather, (and in hot than in cold climates), but it is probable that other factors aid in the production of these diseases beside the high temperature.

Certain epidemic diseases are likewise more frequent in, or exchisively confined to, hot climates. These are cholera, yellow fever and epidemic dysentery. Elephantiasis and the prevalence of certain skin diseases seem also to have some connexion with a constantly high external temperature. The intimate rela-

* A. J. Miles : The Sunstroke Epidemic of Cincinnati, O., during the Summer of 1881. Public Health, Vol. VII., p. 293-304.

tion between cause and effect is not clearly understood, although the belief is current that the origin and spread of such diseases depend upon the development of varU ous parasitic organisms.

Extreme low temperature, as observed in the arctic regions, seems to produce a progressive deterioration of the blood, (anemia), " in consequence of which most natives of temperate regions who are compelled to remain in the far north longer than two winters, succumb to various hemic diseases, scurvy being the most prominent. It is not improbable, however, that the dietary furnished is responsible for a large share of the evil effects ascribed to cold. The absence of sunlight for a considerable part of the winter season, may also have much to do with the bad influences for which the low temperature is held responsible.

Among the acute effects of great cold, frost-bite is the most frequent, as well as the most serious. Loss of portions of the nose, or ears, or even of entire members are not infrequent results of frost-bite.

In the arctic regions, one of the most annoying affections which the traveler has to contend against, is snow-blindness, a severe ophthalmia produced by the glare of the snow. Neutral tinted glass goggles should be worn as a preventive.*

HUMIDITY OF THE ATMOSPHEEE AS CONNECTED WITH CHANGES IN HEALTH.

The propagation of certain acute infectious diseases is believed to be due to a high relative humidity. There can be no longer any doubt that a very humid soil and air, especially if connected with a variable temperature, are almost constant factors in the produc-

* See Pater's Narrative of the Austrian Arctic Voyage of 1872-74, p. 250-3 and 317, for an account of the effects of cold on the organism, and on the best prophylactic measures to be adopted. The Report of the Surgeon General of the V. S. Navy for 1880, also contains (pp. 350-8> a valuable memorandum by Surgeon-General Philip S. Wales, on Arctic Hygiene.

AIR. 11

tion of pulmonary phthisis. Recent experience in this country and abroad has shown that the high plateaus and mountains, far inland, where the soil is dry and the relative humidity of the air low, are the best resorts for consumptives.

Of the effects of excessively dry air on health, little definite is known. It seems probable, however, that catarrhal affections of the respiratory mucous membrane are more frequent in a dry than in a humid climate.

With reference to the influence of electrical conditions of the atmosphere upon health, no observations have been made which admit of definite conclusions being reached.*

Mr. Alexander Buchan and Dr. Arthur Mitchell have analyzed the influence of the weather and season upon the causation of disease, or rather upon the mortality from various diseases, f Taking the records of the city of New York from 1871 to 1877, it appears that the maximum number of deaths from small-pox occurred in May, the minimum in September. From measles there were two annual maxima and minima, the greater in July and September, and the smaller in February and April. From scarlet fever the maximum was in April, the minimum in September. From typhoid fever the maximum was from August to November, the minimum almost equally distributed throughout the rest of the year. From diarrhoea, the maximum in July and August, the minimum from Decern -

* Dr. S. Weir Mitchell has shown (from the record of the case of Gapt. Catlin, U. S. A., see American Journal Med. Sci., April, 1877, and N. T. Med. Jour., Aug. 25, and Sept. 1, 1883), that attacks of neuralgia, in this case at all events, accompanied the progress of storms across the continent. Also, that the periods of maximum pain occurred with a high but falling barometer and increasing absolute humidity. There seems also to be some relation in this case between the maximum pain and the maximum magnetic force as shown by the declinometer. Dr. Mitchell's papers are among the most valuable positive contributions to hygienic meteorology and deserve careful study.

t Journal Scottish Meteorological Society, 1875-8. Abstract in Richardson's Preventive Medicine, Phila., 1884, p. 533, et seq.

ber to March. From diphtheria the maximum in December, the minimum in August.* From whoopingcough, maximum in September and February, minimum in November and June. For croup, the curves agree pretty closely with the diphtheria curves. From phthisis, the maximum in March, minimum in June. From suicide, curiously the greater number occurs in May, the smallest in February. This is contrary to the usual supposition that gloomy weather predisposes to suicide. In Philadelphia, the results of an examination of the statistics of suicide for ten years are almost exactly similar. Out of 636 cases of suicide, 78 occurred in May, 71 in August, 57 in December, 54 each in October, July and April, 52 in June, 49 in November, 44 each in December and February, 43 in March, and 36 in January. f Dr. Lee is led to believe 'that a low barometric pressure, accompanied by a high thermometric registry, with sudden fluctuations from a low to a high temperature, together with much moisture and prevailing south-west winds, might somewhat account for the frequency of self-murder in the spring and summer months. '

THE SANITARY RELATIONS OF CHANGES IN COMPOSITION AND OF IMPURITIES IN THE AIR.

The average proportion of carbonic acid in the atmosphere is from 3 to 5 parts in 10,000. Pettenkofer % places the maximum limit of carbonic acid allowable in the air of dwellings, at 7 parts in 10, 000. It is probable that this limit is very frequently exceeded without serious consequences to health, if the air is not at the same time polluted by organic impurities, the

* See paper on the relation of weather to mortality from diphtheria in Baltimore. By Richard Henrt Thomas, in Trans. Med. and Chir. Faculty of Maryland, 18S3.

t John G. Lee : Suicide in the City and County of Philadelphia during a decade, 1872 to 1881 inclusive. Trans. Am. Med. Asso., Vol. 33, p. 425.

X Quoted in Buck's Hygiene and Public Health, Vol. 1., p. 615.

N AIR. 13

products of respiration. Prof. William Ripley Nichols, found the air in a school-room in Boston to contain eight times the normal proportion of carbonic acid, while Pettenkof er found, also in a school-room, after the same had been occupied two hours, eighteen times the normai proportion, or 72 parts in 10,000.* While such an excess of this poisonous gas must unquestionably have an unfavorable influence upon health, it is probable that the most serious effects are due to the coincident diminution of oxygen and the pollution of the air by the products of respiration which necessarily take place during respiration. Carbonic acid alone may be present in the air to a much greater extent than above mentioned, without causing any appreciable inconvenience. In the air of soda-water manufactories there is frequently as large a proportion as two per cent, of this gas present without producing any ill effects upon those breathing such an atmosphere.

The amount of carbonic acid in the atmosphere is greatest at night. It is also greater very near the ground than at a distance of several feet above it. As carbonic acid is absorbed by the leaves of plants during the daytime, but given off at night, the difference may partly be thus accounted for. According to Fodor,f the source of a large proportion of the carbonic acid in the air, is the decomposition going on in the soil. This accounts for the larger percentage of carbonic acid near the ground. This would also explain the variation of the proportion of carbonic acid in the air under different meteorological conditions. For example, it is found that during rainy weather the carbonic acid in the air is diminished. This is accounted for partly by the absorption of the carbonic acid by the saturated ground,

* See table in Buck's Hygiene and Public Health, Vol. I., p. 612.

while at the same time the porosity of the soil is diminished and the escape of the ground air prevented.

Mr. R. Angus Smith made a number of experiments upon himself to determine the effects of an atmosphere gradually becoming charged with the products of respiration and perspiration. His experiments were conducted in a leaden chamber holding 170 cubic feet of air. This air was not changed during the experiment. After remaining for an hour in this chamber, an unpleasant odor of organic matter was perceptible on moving about. The air when agitated felt soft, owing doubtless to the excess of moisture contained in it. The air soon became very foul, and although not producing any discomfort, the experimenter states that escape from it produced a feeling of extreme pleasure, like 'that which one has when walking home on a fine evening after leaving a room which has been crowded.'*

Hammondf confined a mouse in a large jar in which were suspended several large sponges saturated with baryta water, to remove the carbonic acid as rapidly as formed. Fresh air was supplied as fast as required. The aqueous vapor exhaled was absorbed by chloride of calcium. The mouse died in 4.5 minutes, evidently from the effect of the organic matter in the air of the jar. The presence of this organic matter was demonstrated by passing the air through a solution of potassium permanganate.