EED CORPUSCLES. 119 



tuting what is called the area vasculosa. At first the vessels 

 are filled with a colorless fluid, which soon becomes yellow, 

 and when the embryo is about one-tenth of an inch in length, 

 becomes red, and the corpuscles make their appearance. From 

 this time until the sixth to the eighth week, they are from 

 30 to 100 per cent, larger than in the adult. Most of them 

 are circular, but some are ovoid, and a few are globular. At 

 this period, nearly all of them are provided with a nucleus j 

 but from the first, there are some in which this is wanting. 

 The nucleus is from -^j^ to -g^o- f an ^ ncn ^ n diameter, 

 globular, granular, and insoluble in water and acetic acid. 

 As development advances, these nucleated corpuscles are 

 gradually lost ; but even at the fourth month we may still 

 see a few remaining. After this time they present no ana- 

 tomical differences from the blood-corpuscles in the adult. 



In many works on physiology and microscopic anatomy, 

 we find accounts of the development of the red corpuscles 

 from the colorless corpuscles, or leucocytes, which are sup- 

 posed to become disintegrated, their particles becoming de- 

 veloped into red corpuscles ; but there seems to be no suffi- 

 cient evidence that such a process takes place. The red 

 corpuscles appear before the leucocytes are formed ; 1 and it 

 is only the fact that the two varieties coexist in the blood- 

 vessels which has given rise to such a theory. It is most 

 reasonable to consider that the red corpuscles are formed by 

 a true genesis in the sanguineous blastema. We can offer 

 no satisfactory explanation of the process by which the tissues- 

 are formed from their blastema, nor can we explain the Avay 

 in which the blood-corpuscles, which are true anatomical 

 elements, take their origin. There is furthermore no suffi- 

 cient evidence that any particular organ or organs have the 

 function of producing the blood-corpuscles. Hewson sup- 

 posed that they were formed in the spleen. Kolliker is of 

 the opinion that they are destroyed in the spleen. It is 



1 LONGET, TraitS de Physiologie, tome i., p. 715. 



