XV THE CIRCULATORY SYSTEM 263 



As Bizzozero and Torre have shown, the principal seat of 

 the formation of new corpuscles is in the marrow of the 

 bones. Marquis found that the marrow undergoes periodic 

 changes corresponding to the changes in the blood. In 

 the late spring and early summer, during the period of 

 most active renewal of blood cells, the marrow assumes a 

 lymphoid character ; during the summer it gradually ac- 

 cumulates fat, and retains a fatty character during the fall 

 and winter. During the spring, the fat is more or less 

 completely resorbed, and the lymphoid cells, which are 

 concerned in the formation of new corpuscles, undergo 

 rapid multiplication. 



While most of the corpuscles, both red and white, arise 

 in the marrow of the bones, it is certain that both kinds of 

 cells are also produced by the division of preexisting cells in 

 the circulating blood. This is notably the case in the white 

 corpuscles; and divisions of the young stages of the red 

 corpuscles have been witnessed by a number of observers. 

 The spindle cells from which red corpuscles are derived 

 undergo indirect division, at least after they have acquired 

 hemoglobin. Their transformation into red corpuscles, 

 according to Neumann, occurs only in the spring, after they 

 acquire hemoglobin, but they are present in the blood, 

 although in less numbers, during the whole year. The 

 mature red corpuscles do not divide. The very youngest 

 stage of the red cells is represented, according to Neumann, 

 Dekhuyzen, and others, by small leucocytes with a relatively 

 large nucleus. Transitional stages occur between these and 

 the spindle cells, and between the latter and the young red 

 cells. In their young stages, the red cells have a more or 

 less circular but irregular form, comparatively little hemo- 

 globin, and a relatively large irregular .nucleus. However 

 different the various forms of corpuscles may be in their 



