446 VERA DANCHAKOFF 



structureless masses along with unchanged erythrocytes are also 

 found in the interior of the greatly distended macrophages. 

 This process is illustrated by figures 3 and 4. It extends gradu- 

 ally to larger vessels around the grafts and numerous vascular 

 channels are seen to be distended by these pecuhar thrombi. 



This process of occlusion of the vascular net is followed by 

 necrosis of the previously healthy tissue of the graft. In some 

 cases, however, parts of the graft become necrotic without the 

 described changes having occurred. Microscopic study shows in 

 this case a gradual passage of the necrotic focus into the surround- 

 ing healthy tissue without appreciable reaction around it. 



Heteroplastic tumor as well as homoplastic tissue grafts are 

 equally affected at seventeen to eighteen days of incubation. 

 While the allantois forms a favorable culture medium at the 

 time of the grafting, it gradually and progressively becomes less 

 and less so. These local changes in the milieu, and not the devel- 

 opment of a particular kind of small lymphocyte at a distant point 

 from the tumor growth, seem to bring about the recession of the 

 tumor, as well as that of homogeneous grafts. Even anlages 

 of organs of the same age as the host grafted on the allantois 

 at the seventh to eighth day of incubation begin tcK become 

 necrotic at about the eighteenth day. There is a correlation 

 between the size attained by the graft and the day of incuba- 

 tion at which the graft becomes necrotic, larger grafts becoming 

 necrotic earlier than smaller ones; a small graft may still find 

 sufficient nourishment even in a modified allantois. 



4. GROWTH RESTRAINT OF A TUMOR IN DOUBLE ADJACENT 

 GRAFTS OF TUMOR AND ADULT SPLEEN 



The double grafts of tumor and spleen were made on the 

 allantois with small separate quantities of tumor and spleen 

 mash, practically touching each other. Microscopically, the 

 growing grafts were only seldom found to be in contact during 

 early stages. This is accounted for by the fact that the growing 

 points of the tumor and spleen ~may not necessarily be situated 

 at the place where the tissues come together. The allantoic 

 mesenchyme which separates the two tissues in the first days of 



