116 TEE BLOOD AND ITS CIRCULATION. 



The red globules change very easily : the slightest evapo- 

 ration, the slightest concentration of the liquid in which they 

 float, gives them, by exosmosis, a shrivelled form, indented 

 or crenated (Fig; 32) at the edges, and thus, when seen in 

 front, they present a false impression of an apparent nucleus 

 (Fig.32,/). 



The form, the size, and even the structure of the red glob- 

 ules is not the same in different animals, or even in the same 

 animal at different stages of development. The globules of 

 the human foetus are distinguished from those of the adult 

 by the existence of a nucleus, and it is only towards the 

 second half of the intra-uterine existence that they lose this 

 feature. The blood globules of the adult mammalia are 

 similar in form to those of man, but differ in size : those of 

 the guinea-pig, of the goat, of the sheep, of the horse, and 

 of the rabbit are smaller ; those of the dog, about equal in 

 size ; those of the elephant, much larger. The camel and 

 llama, alone among the mammifera, have globules elliptical 

 in shape, and always without nucleus. In birds the globules 

 are larger than in the mammifera, elliptical and biconvex, 

 and present some traces of a nucleus. The globules of rep- 

 tiles and of the amphibious animals (Fig. 33) are large, 

 elliptical, and biconvex, with a visible nucleus, as is the case 

 generally with fishes. The following figures will be sufficient 

 to give an idea of the differences in size : in man the red 

 globules measure T ^ of a millimetre, and in the proteus -fa. 

 The presence of colored globules in the blood is usually 

 considered a distinguishing feature of vertebrate animals. 

 Rouget has, however, long since pointed 

 out the existence of similar elements 

 in the invertebrate : in this case they 

 are generally without any covering, 

 granulated; and supplied with a coloring 

 matter (hematine, see farther on), which, 

 instead of being uniformly diffused, is 

 present in small distinct quantities. The 

 Fi og^s "biSx? ul ( e i>onn* globules of the sipunculus, however, are 

 "Atlas du ? Cours de composed of a thick, elastic envelope, 



ish, homogeneous substance, which is very refrangent. 



In a physiological point of view the red globules are 

 remarkable for their elasticity : they are slightly and perfectly 

 elastic ; they change their shape on the slightest pressure, 

 but return easily to their original form. In examining the 



