56. THE METHOD OF 

 CHORIOALLANTOIC GRAFTING 



The grafting of early chick embryo parts to the chorio-allantois of an older (8 to 1 day 

 incubated) embryo has long since been perfected (Hoadley, 1924, Willier, 1924). The 

 highly vascularized chorio-allantois of the avian embryo is located close to the shell 

 membrane of an 8-day embryo, so that the shell over it can be removed and the explant 

 can be placed upon it as a substrate for nutrition and growth. If the shell is replaced and 

 sealed into place with melted paraffin, the explant will generally become vascularized 

 and will develop for 9 to 1 days and may be recovered before the natural breakdown of 

 the extra-embryonic membranes on the 19th day of incubation. 



Chick egg with window above the develop- 

 ing embryo. Black washer is sealed to the 

 egg shell and to the covering coverglass 

 with paraffin. Irregular margin of torn 

 shell membrane visible through the window. 

 Embryo can develop and hatch. 



Hen's egg showing attached window 

 through which the development of the 

 embryo can be observed. 



(Courtesy General Biological 

 Supply House, Chicago. ) 



Since there is complete isolation of the explant, there are no persistent inductive influ- 

 ences. However, the explant does come under the hormonal and other influences ema- 

 nating from the blood of the host, and these must be considered. Further, there is a 

 space limitation (within the host environment) and the further possibility that the graft 

 may develop a parasitic relationship to the host, thereby utilizing some of the nutritional 

 requisites of the host and indirectly alter the normality of the host environment. 



Nevertheless, the chorio-allantois is proving of value in the study of mammalian isolates 

 (Nicholas and Rudnick, 1933) and in the culturing of bacteria and viruses (Goodpasture, 

 1938). Experience has indicated that the 48 hour eye and the 72 hour limb are the most 

 satisfactory anlage to transplant. 



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