ERYTHROBLASTS IN THE PIG EMBRYO 11^1 



and cytoplasmic fixation and stain of both nucleated and non- 

 nucleated blood elements appeared excellent. 



To decide this question it therefore became necessary to ex- 

 amine the fresh membranes directly and ascertain the form of 

 the cells as they occur in the plasma while circulating through 

 the living vessels. This was done at the abattoir. The embryos 

 and membranes were removed from the uteri with the greatest 

 possible economy of time, while the heart was still beating vig- 

 orously. A part of the foetal membrane was laid upon a slide 

 on the stage of a microscope placed in a warm chamber, and the 

 contents of the vessels at once examined. For this purpose the 

 amniotic membranes proved the most favorable because of their 

 transparency and ease of manipulation with the least disturbance 

 to the contained vessels. It soon became evident that the ma- 

 jority of large nucleated erythroblasts in the vessels and capil- 

 laries of the membranes (of 25 to 35 mm. embryos) were typically 

 nucleated biconcave discs, while others were more or less bi- 

 concave — convex or bell-shaped. In favorable regions where the 

 circulation was sufficiently retarded- beautiful views of the blood 

 corpuscles could be obtained as they passed a given point in the 

 blood channel. This was especially true in one instance where an 

 angle of a small vessel lay in the field of the microscope and the 

 corpuscles could be followed as they passed around this angle in 

 the vessel. The nature of the angle and the direction of the current 

 were such that in the majority of cases the large nucleated erythro- 

 blasts almost in single file were regularly turned completely over 

 before passing entirely around the angle. During one stage of the 

 process of turning over, the erythroblasts almost invariably pre- 

 sented for a moment a biconcave or cupshaped profile. An instant 

 later the same cell, upon presenting a flat view would assume the 

 strikingly deceptive appearance of being spherical. Scores of 

 erythroblasts were observed in this manner, always with similar 

 results. 



- It should be explained that in making these preparations the vessels had neces- 

 sarily been severed in their connections with the heart so that the circulation re- 

 ferred to was in the nature of a streaming of the plasma in the vessel rather than 

 a movement due to the beating of the heart. 



