No. 1.] BLOOD CORPUSCLES. 



69 



heart or in some other way. In any case, they were extremely 

 few in number, and did not resemble the white corpuscles of the 

 grown animal. The blood plates also were entirely absent from 

 the blood of this embryo. Not a single specimen could be found, 

 though a number of preparations were examined. It seems to 

 me that this fact has a bearing upon the theories of the origin 

 of this element, and I shall refer to it again when discussing 

 that subject. In a human embryo of five months, both white 

 corpuscles and blood plates were found, though both were pres- 

 ent in small numbers. The white corpuscles were of two 

 kinds, as in the adult, — one variety of small size, with a single 

 vesicular nucleus resembling the lymphocytes ; and the other 

 of larger size, faintly granular, with several nuclei, or, more 

 correctly, with a fragmented nucleus. At this age in the 

 hum.an embryo, the great majority of the red corpuscles have 

 lost their nuclei. In a cat embryo of 9 cm. length the leuco- 

 cytes and blood plates were both found, though the former 

 were present in small numbers. I have not been able to find 

 any special reference to the occurrence of these elements in 

 the foetal blood, except in a paper by Neumann (5(f/). In the 

 examination of human foetuses made by Neumann, he states 

 that generally the white corpuscles were very few in number, 

 but makes no reference to the variations with the age of the 

 foetus. The fact that the white corpuscles are so late in 

 appearing is important, not only in its bearing upon the old 

 theory that they become changed into red corpuscles, but also 

 in the fact that it furnishes a means of determining their influ- 

 ence upon the chemical composition of the plasma. 



II. Formation of Red Corpuscles during Extra- 

 uterine Life. 



Historical Review, 



The greater portion of the literature of the red blood cor- 

 puscles bears upon this side of the subject. Very many dif- 

 ferent views have been proposed ; and a brief presentation of 

 the most important of them may be of value, both as an indica- 

 tion of the drift of opinion upon the subject, and also to enable 

 me to present my own work afterwards in the briefest possible 

 way, without detailed reference to or comparison with other 



