A STUDY OF THE BLOOD 



127 



have circular red disks, with the exception of the camel 

 family, in which they are oval. In a given species of ani- 

 mals the diameter of red corpuscles is pretty constant, but 

 one finds great variations in size in a comparative study. A 

 kind of amphibian (Proteus) has the largest known corpus- 

 cles; the smallest are found in the musk deer. Among 

 birds the size is proportional to the size of the animal, being 

 largest in the ostrich and smallest in the humming bird. 



In murder trials a practical use is made of these striking 

 differences in red blood corpuscles. If blood stains are found 

 on an implement or an article of clothing, microscopical ex- 

 amination can sometimes decide to what animal the corpus- 

 cles belong, and in many cases this evidence decides whether 

 there shall be conviction or acquittal of the accused. 



6. CHEMICAL COMPOSITION OF BLOOD 

 A. Solid ingredients. 



1. Red corpuscles, composed of 



a. Water, 50%. 



b. Hemoglobin, over 35%. 



c. Mineral matter, etc., 5%. 



2. White corpuscles, composed of 



a. Water. 



b. Proteids. 



c. Mineral matter. 



B. Liquid ingredient == blood plasma, composed 



of 

 1. Fibrinogen, which changes to fibrin, 



Forming 



the 

 Blood 

 Clot. 



2. Blood serum, composed of 



a. Water, about 90% < 



b. Proteids, about 8% to 



Absorbed 



from 



Alimentary 

 Canal. * 



c. Fats, sugars, and mineral matters, 



from 2% to 1% < 



d. Urea and water, wastes obtained from tissues 



and carried to excretory organs. 



