58 NORMAL HISTOLOGY. 



it is an animal) is the one generally accepted. This organism at- 

 tacks the red corpuscles, destroying the haemaglobin. It may be 

 stained with methylene-blue, aqueous or alcoholic solution, and can 

 be detected as a minute body, irregular in shape, filling about one- 

 fourth of the corpuscle. Its life history includes five distinct stages : 

 (1) The spore; (2) the protoplasmic, or fission, stage; (3) the 

 amoeboid form; (4) the plasmodium, consisting of several amoeboid 

 forms united; (5) the encysted stage, containing a cell- wall within 

 which the cell contents break up into spores. This cycle of changes 

 through which the organism passes accounts for the fact that per- 

 sons afflicted with malaria experience a recurrence of the symptoms 

 at stated intervals. 



Laboratory exercise No. 12. Corpuscles., rouleaux, and fibrils of 

 fibrin. Clean a slide and cover-glass. This step should precede nearly 

 all the exercises that follow. Wrap the ring finger with a kerchief 

 from the base to the first joint. Apply a few drops of alcohol to cleanse 

 the exposed surface, and then, with a lance or sterilized needle, with a 

 quick motion puncture the skin just above the root of the nail. Wipe 

 off the first drop of blood, and to the next apply the surface of a cover- 

 glass. Place this upon a slide, blood down. Now examine with H. P., 

 observing first the red corpuscles, which will be found to be collecting 

 by their flat surfaces into rows, called rouleaux. Examine one of the 

 discs on edge, then in profile. With fine adjustment focus up and down. 

 Why does the center of the disc appear alternately dark and light? 

 Examine now the platelets and leucocytes. They may be found in the 

 clear spaces between the red discs, and, as they adhere to the glass, do 

 not float about in the serum. Lay aside this preparation until the next 

 period and examine for the fibrils of fibrin, which will appear as deli- 

 cate threads beneath the cover-glass. 



Crenation and Amoeboid Movement. Make a second preparation by 

 the method above described. Add to the blood a small drop of normal 

 saline. Examine and observe the crenated appearance of the colored 

 discs. This is due to exosmosis. Gently warm the slide and look for 

 the amoeboid movement of the leucocytes. To observe this may re- 

 quire that the slide be kept warm for a considerable period. 



Acetic acid brings into view the nuclei of leucocytes. Water removes 

 the ha?maglobin from red corpuscles, while sirup causes the disc to 

 shrivel. 



Laboratory exercise No. 13. Preparation of a blood slide. Secure a 

 drop of blood by the method described, and apply a clean cover-glass. 

 To this apply a second cover-glass, and with gentle pressure spread out 

 the blood. Then, with a quick motion, keeping the cover-glasses paral- 

 lel, draw them apart so as to leave a thin film of blood on each. Select 

 the best preparation, lay it upon a piece of writing paper, blood up, and 



