EQUIVALENCE OF HEMATOPOIETIC ANLAGES, I. SPLEEN 269 



transplanted tissue ideal conditions in supplying the growing 

 tissue \^^th nutritive material and also in withdrawing the pro- 

 ducts of the metabolism of the developing and differentiating 

 cells. Though the tissue growth and differentiation cannot 

 be observed right under the microscope, this is compensated by 

 the facility of obtaining abundant experimental material in 

 dilTerent development stages. 



As Murphy and Rous (30), I used the method developed 

 by Peebles for studies in experimental embryology. Since I had 

 to overcome many difficulties, and failures were due sometimes 

 to apparently minute details, I will undertake a thorough de- 

 scription of the culture-method on the allantois of the chick 

 embryo, as I used it in my experiments. I am indebted to the 

 kind efforts of Mr. Ebeling of the Rockefeller Institute for being 

 supplied through the whole winter with fertilized eggs, which 

 developed in the incubator in the number of 60 to 70 per cent. 

 The cultures succeed on the allantois easily from the beginning 

 of the 7th day of incubation. The cultures of the hematopoietic 

 organs grow if in contact with the mesodermal surface of. the 

 allantois. The ectoderm, which overlies the area vasculosa 

 and the 3'olk does not offer favorable conditions for cultures of 

 hematopoietic tissue. From the 7th day of incubation, however, 

 the allantois appears as a well-sized sac, flattened under the egg- 

 shell. 



It is easy to determine by means of illumination, which of 

 the incubated eggs started to develop. The localization of the 

 embryo body as well as that of the allantois with its vessels 

 comes therebj^ clearly out. Good places to choose for grafting 

 are regions between the junction of two vessels at a distance of 

 1 to 2 cm. £rom the embryo body. The illumination and the 

 provisional marking of the eggs must be done quickly and the 

 eggs immediately returned to the incubator. A sawing out of 

 small windows in the region marked on the eggshell follows. It 

 is advisable to saw the windows in the form of a trapezium, 

 which form allows to orientate it easily, when the window has 

 to be closed. A great care must be observed in sawing the win- 

 dows out of the eggshell. The pressure of the instrument has 



