100 PHYSIOLOGY CHAP. 



It goes without saying that the quantity of blood must vary 

 with the constitution, sex, age, state of nutrition, and with many 

 other functional or purely individual factors. Clearly, lymphatic 

 individuals and those whose fatty tissues (which are poorest in 

 blood) are strongly developed, must have a considerably lessf 

 quantity of blood than other individuals in whom muscular 

 tissues which are richly irrigated with blood predominate. The 

 former may be relatively termed anaemic, the latter plethoric. 



VI. The morphological study of the blood is founded on micro- 

 scopical observations, which show the presence of three distinct 

 elements lied Corpuscles (Erythrocytes or Haemacytes), White 

 Corpuscles (Leucocytes), and Platelets (Hayeni's Haematoblasts). 



The Erythrocytes are in the form of biconcave discs, non- 

 nucleated and round in all mammals (save the camel and the llama, 



FIG. 26. Form and relative size of erythrocytes of different animals, viewed from the 'surface. 

 1. Erythrocyte of musk-deer ; 2, goal; 3, marmot; 4, llama; '>. man; <], pigeon; 7, tench; 

 8, lizard ; 9, frog ; 10, proteus. 



in which they are elliptical) ; nucleated and elliptical in birds, 

 reptiles, amphibia and fishes (Fig. 26). The red corpuscles of 

 man have a diameter of 7-8 ^ and a depth of 1'7 /x ; in other 

 mammalian animals they are even smaller; in birds and the 

 lower vertebrates they are much bigger (21 /x in frog, 29 /x in 

 Triton, 58 /x in Proteus). Viewed from above, and isolated, they 

 are greenish-yellow in colour ; seen from the side as a rouleau of 

 discs, they are red (Fig. 27) ; to them the blood owes its char- 

 acteristic colour, and they render it opaque. They are soft, 

 almost gelatinous in consistency hence they easily change their 

 shape ; but they are perfectly elastic, and recover their original 

 form directly the contracting force ceases to act on them. 



Pted corpuscles may be divided, according to their affinity for 

 staining, into orthochrornatic and polychromatic (Ehrlich). The 

 orthochromatic are the most numerous, and stain with aurantia 

 and eosin. The polychromatic, which are much less frequent, 

 take up fuchsin when they are stained with tri-acid ; with eosin- 

 methylene-blue they stain violet, etc. Red corpuscles are classified 



