166 VICTOR E. EMMEL 



the origin of the plastids from the mature erythroblasts, especially 

 in blood taken at a time when such changes are at their height in 

 the circulation as in the case of the embryos studied. Concerning 

 the maintenance of the blood cells in vitro it is of interest to note 

 that Jolly ('11) who succeeded in keeping leucocytes from the 

 frog's blood alive for nearly twelve months, found these cells 

 still vitally active under conditions in which there had occurred 

 considerable hemolysis and degeneration of many of the other 

 blood corpuscles in the plasma. In his account of the experiment 

 he states: 



Dans les tubes, il existait une hemolyse plus on moins considerable et 

 de nombreuses cellules etaint detruites. Bien que les leucocytes aient 

 trouve dans ces elements, qu' ils phagocytent activement, une riserve 

 de nourriture abondante, il est vraiment remarquable de les voir con- 

 tinuer de vivre dans um milieu contenant des prodiiits d' autolyse et qu' 

 au premier abord on pourrait penser leur etre nuisible (p. 147-148). 



4. EVIDENCE CONCERNING THE ORIGIN OF PLASTIDS IN THE EM- 

 BRYO BY A SIMILAR PROCESS OF CYTOPLASMIC CONSTRICTION 



a. In the living vessels 



Regarding the preceding discussion it is not to be overlooked that 

 the final decision concerning the normal character of the mode of 

 plastid formation observed in vitro must be based to an important 

 degree upon the evidence indicating the actual occurrence of 

 the same process within the vascular system of the embryo. 

 Attention has already been called to the observation of the for- 

 mation of plastids by cytoplasmic constrictions in the fresh 

 cultures immediately after their preparation (fig. 13). Having 

 seen these changes in the blood just removed from the vessels, an 

 attempt was next made to ascertain whether' similar processes 

 could be observed within the fresh vessels. For this purpose pig 

 uteri were brought into a warm operating chamber at the slaughter 

 house within a few minutes after the killing of the parent animal. 

 All the operations were carried on within this warm chamber at 

 a temperature approximating 38 to 40°. The procedure consisted 

 in opening the uteri, laying the foetal membrane over a clean slide 

 placed upon the warm stage of the microscope, and the prepara- 



