Laboratory directions in histology; a guide for use in a laboratory course in histology

Front matter

LABORATORY DIRECTIONS

IN HISTOLOGY

HISTOLOGICAL TECHNIQUE

Contents

Introductory 7

The Microscope 9

The Cell 11

II The Cell

1. {Preparation No. ) The Vegetable Cell. From the inner' side of one of the layers of an onion strip off a piece of the cuticle (skin) and place it on a slide in a drop of dilute methyl green (stain). Cover it. Permit it to remain for a few minutes and in the meantime, place another piece upon a slide in a drop of water ; cover and examine. Be prepared to describe what you see. Eem&ve the eoverglass and add a drop of iodine solution : replace the eoverglass and examine. Result. Sketch a few cell- walls, nuclei, cytoplasm (cell-body). If desired, a drop of sulphuric acid may now be placed at the edge of the eoverglass so that it may lun under and reach some portion of the specimen. The plant cell-wall (cellulose) will be turned blue.

Examine the piece of plant membrane that has been standing in dilute methyl green. What has been the result? How do you explain it? (General chemistry of staining; classification of stains; the value or advantage of staining.) Methyl green is a stain of the same general kind (basic, nuclear) as the hematoxylin used largely in this course.

2. (Preparation No. ). The animal cell. Repeat the experiments given under No. 1 with a piece of cast "skin" of a frog or other animal tissue given you. Sketch a few cells. Compare the results with those secured with the plant tissue.

What is the general appearance of the cell Protoplasm and Nucleus in the fresh condition? A further study or analysis of the structure of the cell is postponed until later in the work.

Ill

THE CELLULAR ORIGIN OP THE BODY.

The preparations studied in this exercise are all stained preparations from "fixed" (Technique ) tissue. This should be well appreciated as well as what is involved in fixing and staining.

3. [Preparation No. ). The Egg-Cell or Ovum. Study a section of Ovary of a Starfish and identify the large roughly oval egg-cells. Select one or two of the best preserved and stained whii'h are cut through the middle and sketch carefully, naming all parts (nucleus, cell-body; nuclear membrane, cell-membrane, nucleolus, chromatin network, character of the cytoplasm).

4. (Preparation No. ) . The Mammalian Ovum. In the section of an ovary, search out an Ovum (Oocyte) that shows well and sketch. Compare with No. 3.

5. (Preparation No. ). The Spermatozoon. It is unnecessary to consider the structure beyond the recognition of tail, middle-piece and head, which last embodies a cell-nucleus.

6. (Preparation No. ). Fertilization. Prom a section of the egg-tube of the round-worm of the horse, Ascaris, sketch an egg showing side by side, two nuclei, — the egg-nucleus and the sperm-nucleus derived from the Spermatozoon.

7. (Preparation No. ). The Ovum of Ambystoma (salamander) divided into a few cells : — Early Blastula Stage. Sketch this showing cells and nuclei in outline only. The cells are so large that the nucleus may or may not appear in the section. The yolk granules (stored food-material; paraplasm (deutoplasm) give the cells their characteristic appearance; draw these in a portion of one of the cells. Can you see the cell-protoplasm?

8. (Preparation No. ). The Ovum of Ambystoma divided into many cells; — Late Blastula Stage. The continued division of the cells and their nuclei have increased their number but decreased their size.