THE BLOOD. 



59 



corpuscles to elbow their way through the delicate capil- 

 lary channels. 



7. The Origin of the Red Corpuscles. One of the 

 most difficult chapters in physiology is that dealing with 

 the origin of the red corpuscles, and a number of conflict- 

 ing theories are even now seeking support. To trace the 

 origin of the red corpuscles it is necessary to study the 

 blood of an animal before its birth. Such examination of 

 human embryos shows that in early uterine life the red cor- 

 puscles are nucleated and possess the power of amoeboid 

 movement. They are, in fact, very similar to the white 

 corpuscles of the blood except that they are colored with 

 haemoglobin. These corpuscles arise in this way: 



Some of the connective tissue cells become somewhat 

 elongated and have their nuclei divide up into many 



Fig. 12. EMBRYONIC DEVELOPMENT OP BLOOD CORPUSCLES IN CONNECTIVE TISSUE 



CELLS, AND THE TRANSFORMATION OF THE LATTER INTO BLOOD CAPILLARIES. (After 



Schafer.) 



, an elongated cell with fluid protoplasm and containing corpuscles which are still 

 round; 6, a more hollowed cell in which the corpuscles have become disc-shaped; c, the 

 manner of union of such a tissue cell (c ft) containing here only one corpuscle with an 

 already formed capillary, (a and c from a new-born rat, 6 from a fostal sheep.) 



smaller nuclei. These nuclei soon seem to round them- 

 selves, become tinted red with haemoglobin, and are in fact 

 the nucleated red corpuscles of the embryo. The connective 



