ERYTHROBLASTS IN THE PIG EMBRYO 151 



of the behavior of blood corpuscles in plasma cultures was begun 

 somewhat over two years ago, some of the results of which, in so 

 far as they relate to the question of the origin of the non-nucle- 

 ated erythrocytes in the early pig embryo, will be here presented. 



a. Material and methods 



The material studied consisted chiefly of pig embryos from 25 to 

 35 mm. in length. At this time there occurs within the embryonic 

 circulation a marked increase in the number of non-nucleated 

 erythrocytes, so that whereas the blood of younger embryos 

 consists almost entirely of nucleated corpuscles, the non-nucleated 

 elements predominate in older specimens. Consequently, pig 

 embryos approximating 30 mm. in length, might be expected to 

 prove especially favorable for the investigation of the processes 

 involved in the origin of the non-nucleated erythrocytes. 



Through the kindness of the Krey Packing Company of St. 

 Louis these embryos could be obtained under very favorable 

 circumstances, so that the embryos could be removed from the 

 uteri and the blood obtained within a few minutes after the kill- 

 ing of the parent animal. For some purposes the material was 

 at once placed in a warm chamber set up at the abattoir. Within 

 this chamber, maintained at 38 to 40°C., preparations of the 

 blood as well as of the foetal membranes and their vessels could 

 be immediately examined microscopically. More permanent 

 cultures necessitated an incubator. For this purpose the preg- 

 nant uteri were removed to the Anatomical Laboratory of the 

 Medical School. An apparatus based on the principle of the 

 fireless cooker rendered it possible to make this transfer of the 

 fresh material with little deviation from the normal body temper- 

 ature, which in a preliminary examination of fifteen uteri just 

 taken from the slaughtered animals^ had been ascertained to range 

 from 37 to 40°. A self-registering maximum-minimum thermom- 

 eter was always carried with the specimens. The entire time elaps- 

 ing between the taking of the uteri and their arrival at the labor- 

 atory occupied from thirty to forty minutes. Only embryos in 

 apparently perfectly normal condition, with the heart still beat- 

 ing, were used for culture purposes. 



