110 THE BLOOD 



that any anemia must be due to abnormal conditions. Post-partum anemia 

 should not last longer than two weeks. 



The red corpuscles are not all alike. In almost every specimen of blood 

 a certain number of corpuscles smaller than the rest may be observed. They 

 are termed microcytes, or hematoblasts, and are probably immature corpuscles. 



A peculiar property of the red corpuscles, which is exaggerated in in- 

 flammatory blood, may be here again noticed, i.e., their great tendency to 

 adhere together in rolls or columns (rouleaux), like piles of coins. These 

 rolls quickly fasten together by their ends, and cluster; so that, when the 

 blood is spread out thinly on a glass, they form a kind of irregular network, 

 with crowds of corpuscles at the several points corresponding with the knots 

 of the net, figure 109. Hence the clot formed in such a thin layer of blood 

 looks mottled with blotches of pink upon a white ground. 



The red corpuscles are constantly undergoing disintegration in different 

 parts of the circulatory system, particularly in the spleen. The liberated 

 hemoglobin contributes to the formation of the bile pigments in the liver. 



Development of the Red Blood-Corpuscles. The first formed 

 blood-corpuscles of the human embryo differ much in their general characters 



FIG. 112. Part of the Network of Developing Blood- Vessels in the Vascular Area of aGuinea- 

 Pig. bl, Blood-corpuscles becoming free in an enlarged and hollowed-out part of the network; a, 

 process of protoplasm. (E. A. Schafer.) 



from those which belong to the later periods of intra-uterine, and to all periods 

 of extra-uterine life. Their manner of origin is at first very simple. 



Surrounding the early embryo is a circular area, called the vascular area, 

 in which the first rudiments of the blood-vessels and blood-corpuscles are 

 developed. Here the nucleated embryonal cells of the mesoblast, from 

 which the blood-vessels and corpuscles are to be formed, send out processes 

 in various directions, and these, joining together, form an irregular mesh- 

 work. The nuclei increase in number, and collect chiefly in the larger masses 

 of protoplasm, but partly also in the processes. It appears that hemo- 



