48 PRACTICAL MICROSCOPY. 



Certain changes in form result, after removal from the circulation, 

 yiz. : 1. They may adhere by their broad surfaces forming columns. 

 2. From shrinkage they may become crenated. 3. Still further 

 shrinkage produces the chestnut-burr appearance. 4. From absorp- 

 tion of water they may swell irregularly, obliterating the concavity of 

 one side. 5. From continuous absorption they swell, forming spheres 

 which are finally dissolved. 



Wind a twisted handkerchief tightly around the left ring finger ; 



w 



FIG. 32. DIAGRAM OF A COLORED BLOOD-CORPUSCLE, SIDE VIEW SHOWING THE BI-CONCAVITY. 



A, B, Upper plane; which, in focus, gives the appearance shown at G, Fig. 31. 

 C, D, Plane giving the appearance F, Fig. 31. 



prick the end with a clean needle, and squeeze a minute drop of blood 

 on a slide, add a drop of saliva, cover and focus M. 



Observe : 1. That considerable variation in size of the red blood- 

 corpuscles exists. 2. The color a delicate straw tint. 3. That the 

 concave centre of the corpuscles which lie flat can be made to appear 

 alternately dark and light according to the focal adjustment. 4. That 

 the concavity is also demonstrated as the corpuscles are turned over by 

 the thermal currents.* 



BLOOD-PLATES. 



Minute corpuscular elements in the blood about one-fourth the size 

 of the red discs exist in the proportion of about one of the former to 

 twenty of the latter. They are colorless ovoid discs; and are regarded 

 by Osier as an essential factor in the coagulation of the blood. 



Prick the thoroughly clean finger with a needle. Over the puncture 

 place a drop of solution of osmic acid (vide formulae) and squeeze out 

 a minute drop of blood so that, as it flows, it is covered by the acid 

 solution. This fixes the anatomical elements, providing against 

 further change. The blood, as soon as drawn, must, with the acid, be 



* The student is at this time advised to study the corpuscular elements of 

 the blood of such animals as he may be able to command. The red corpuscles 

 of mammals (excepting the camelidse) do not vary in appearance from those 

 of man, excepting in size. Those of birds, fishes, and reptiles are elliptical 

 with oval nuclei. Corpuscles of the blood of invertebrates are not colored. 



