SECT. 6] OF THE EMBRYO 933 



curve from these biochemical data, and see how well they agreed 

 with the curve obtained by Murray. The curve so resulting is placed 

 beside Murray's in Fig. 253. His smoothed curve is S-shaped, but that 

 calculated from the chemical analyses tends rather to be uninflected. 

 Considering the many operations involved in the establishing of the 

 chemical curve the agreement is good, but it is not possible to decide 

 which curve is the more reliable. 



The consumption of food, as Murray pointed out, is enormous in 

 the early periods. On the 6th day, for instance, the embryo absorbs 

 over its own mass of dry solid, which would be equivalent to an 

 adult man eating about 1 50 pounds of food per day. During the 

 time between the 6th and the i8th days of incubation, this rate falls 

 to about a quarter of its original value. According to Lotka, a 

 mature meadow-lark consumes about 6-6 of its own weight in one 

 day, so that the fall in absorption rate must continue for a consider- 

 able time after hatching. 



A few words may be included at this point about the routes of 

 absorption of material by the embryo, for the subject is not wholly 

 of morphological importance. Wislocki injected trypan blue into the 

 air-chamber, yolk-sac, allantoic and amniotic sacs, and allantoic 

 mesoblast at 11 days' incubation. On opening 2 days later, no 

 staining of embryo or membranes was observed after injections into 

 the air-chamber, but the trypan blue in the yolk was absorbed 

 vigorously by the epithelial cells lining the interior of the yolk-sac. 

 Eventually the dye penetrated the basement membrane on which 

 the endoderm rests, and reached its final destination in groups of cells 

 surrounding the rich venous network in the yolk-sac wall. It did not 

 pass into the vessels and so to the embryo, but it well illustrated how 

 other substances would do so. In spite of the connection between 

 the yolk-sac and the intestinal lumen through the vitelline duct no 

 trypan blue passed into the embryo by that means. From the allantoic 

 cavity no absorption of trypan blue occurred. From the amniotic 

 cavity there was some passage of the dye into the intestines but no 

 other absorption, Hammar next reported a few generally similar 

 results with neutral red & cresyl blue, and Hanan later continued 

 these studies with trypan blue and methylene blue. Making injec- 

 tions into the air-space and examining the egg at varying periods 

 subsequently, he found that as a rule the stain appeared in the egg- 

 white, the allantoic Hquid and membrane, and in the embryo, 



