96 BLOOD AND LYMPH. 



blood are all perfect and show no visible signs of degenera- 

 tion. What becomes of them when they decay and how they 

 are removed from the circulating blood is not entirely known, 

 but it is supposed that the spleen and liver, especially the 

 former, are important agents in their removal and destruc- 

 tion. 



Differences in vertebrate red blood-corpuscles : Red corpus- 

 cles occur only in the blood of vertebrates, that of inverte- 

 brates containing only colorless corpuscles. The different 

 classes of vertebrates exhibit differences in the characters of 

 the erythrocytes with regard to shape, nucleation, and size. 

 All mammals, like man, have non- nucleated biconcave circu- 

 lar red corpuscles, except the camel family, in which they are 

 elliptical (and non-nucleated). In the birds, reptiles, am- 

 phibians, and fishes, the red corpuscles are elliptical, nu- 

 cleated, and biconvex (the nucleus causing an expansion of 

 the corpuscle), except in the cyclostomata or lampreys among 

 fishes, whose corpuscles are circular. 



As to size, the erythrocytes of mammals are the smallest, 

 those of amphibians the largest. 



Among mammals the red cell of the elephant is the largest 

 (9.2 // in diameter), that of the musk-deer the smallest ; and 

 it is the smallest known of all animals (2.5 //). Human 

 erythrocytes are among the largest of those of mammalia. 

 The erythrocytes of birds and fishes are much the same in 

 size; the corpuscle of the fowl is about 12 /j. long, of the 

 pigeon 15 //, of the carp 13 p. The frog's red corpuscles are 

 about 16 by 22 /Jt; those of the amphibian proteus 35 by 58 

 //. ; while those of the amphibian amphiuma are about 46 fj. 

 wide by 77 // long, the largest known, and visible to the 

 naked eye. 



The number of the erythrocytes is in general in an inverse 

 proportion to their size, the smaller cells occurring in greater 

 numbers ; thus, the red corpuscles of the frog number only 

 404,000, those of the proteus 36,000 to the cubic millimetre. 

 Owing to this inverse relation of number and size the total 

 mass of corpuscles in equal volumes of blood is somewhat 

 equalized ; but the greater the number of corpuscles the 

 greater is their total surface ; and the greater their surface (as 

 in birds) the more active is the metabolism. 



