DIGESTIVE ACTIVITY OF MESENCHYME 439 



were deposited on the allantois at seven days of incubation, and 

 two to four eggs opened every twenty-four liours. 



Macroscopically, the grafts were found already estabhshed 

 within twenty-four hours. They enlarged steadily for eight 

 to nine days. From that time on, no further growth could be 

 demonstrated, and at about two to three days before hatching, 

 the tumor was seen to become opaque and necrotic and to assume 

 a yellowish tint. 



The microscopical study of a tumor graft twenty-four hours 

 after grafting shows that, as has been found in the study of the 

 splenic grafts, only that part of the graft survives which is in 

 close touch with the membrane. At the time of the grafting 

 (seven days of incubation) the allantois is covered by an unin- 

 terrupted epithelial layer of the ectoderm of the serosa, which 

 rarely offers sufficient mechanical resistance to prevent the 

 take of the graft. Twenty-four hours after grafting, tumor 

 cells adjacent to the allantois are already in contact with the 

 mesodermal constituents, the epithelial covering of the serosa 

 having become interrupted in many places. Tumor cells undergo 

 frequent mitoses, especially along the channels of the rich vas- 

 cular net. They round up during the process, but during the 

 resting stage they send out numerous long and slender processes 

 into the depth of the allantois. The sudden appearance of the 

 tumor cell does not call forth any appreciable reaction in 

 the allantoic tissue. The grafted tissue having come into 

 contact with the allantois over an area of about 1 to 4 sq.mm., 

 numerous tumor cells find access into the allantois and become 

 the starting-point of a proliferating neoplasm. The graft is 

 seen sometimes to break as a whole through the epithelial layer 

 of the allantois, and both surviving cells and necrotic masses 

 lie within an edematous allantois. 



Numerous interesting details are observed in parts of the 

 graft which do not come into immediate contact with the allan- 

 toic tissue. Not all of the tumor cells undergo a process of 

 necrosis and disintegration, though many of them do. A number 

 of tumor cells, however, even originally at a certain distance 

 from the vascularized mesenchyme, survive and show themselves 



