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STUDIES IN PHYSIOLOGY 



toads), and fishes are called cold-blooded animals. In re- 

 ality these animals have the same temperature as their sur- 

 roundings, and since these surroundings are usually cooler 

 than the 981 of man, these animals feel cold to the touch. 

 White Corpuscles Even in colorless blood there are cells 

 corresponding to the white corpuscles of man which have 

 the power of altering their form by amoeboid movement. 



FIQ. 46. A Comparison of Red Corpuscles. 



We may, then, regard white corpuscles as a constant con- 

 stituent of blood in all animals. 



Red Corpuscles. Ked corpuscles are found in nearly all 

 vertebrates and in vertebrates only; but in the various groups 

 there are striking differences in their form and size. Fishes, 

 amphibia, reptiles, and birds usually have oval red corpus- 

 cles which always have a nucleus. In man and other 

 mammals no nucleus is seen in completely formed corpus- 

 cles, although the cells in the red marrow of bones from 

 which they are formed do have a nucleus. All mammals 



