THE BLOOD. 25 



Are the red corpuscles the same in man as in the animals? 



In mammals the general character of the corpuscles is the same 

 as in man, but the size of the corpuscles varies in different animals. 

 In reptiles, fishes, and birds the red corpuscles are oval, nucleated, 

 and usually are larger than those of mammals. 



What are microcytes? 



In many specimens of blood are observed some corpuscles which 

 are smaller than the rest : they are called microcytcs, and are 

 probably immature corpuscles. One form is of especial interest. 

 They are of about one-third the size of ordinary corpuscles, not 

 deeply pigmented, round or oval. They are called the blood-plates 

 of Bizzozero, and have been affirmed to be broken up to form the 

 fibrin ferment. 



What is the origin of the colored corpuscles ? 



This is somewhat uncertain, but it is probable that red corpuscles 

 take their origin from colorless nucleated corpuscles similar to if 

 not identical with white corpuscles ; possibly also from the nuclei 

 of white globules, from the tissue of the spleen, and from the 

 marrow of the bones. 



How are the red corpuscles destroyed? 



Without doubt, the red corpuscles have a definite life, and when 

 their work is done die as do the other parts of the body, after a 

 tolerably definite existence. Neither the length of their life nor 

 the manner of their death is definitely understood. It is believed, 

 and partially demonstrated, that they undergo disintegration in the 

 spleen. 

 What is the number of the red blood-corpuscles ? 



It is almost beyond estimate, but it is calculated that the aver- 

 age for normal human blood is about 5,000,000 in each cubic 

 millimetre. In practice it is customary to estimate the number 

 of red corpuscles by counting the corpuscles in a minute but 

 measured quantity of blood spread upon a ruled microscope slide. 

 Such an instrument is known as a haemocytometer, and that of 

 Gowers is frequently used. 



Describe the white or colorless blood-corpuscles. 



They are spherical, granular masses of protoplasm, possessing 

 a nucleus, but no cell-wall. They are about ^QTT i- ^ n diameter, 

 though some appear smaller, and are probably undeveloped white 

 corpuscles. 



