Influence of Temperature upon Pepsin. 



75 



become somewhat more "virulent" in that such tumors grow 

 more rapidly and produce more extensive metastases of a more 

 epithelial type. 



Animals that have failed to take the first inoculation of tumor 

 are very seldom susceptible to a second or third implantation. 

 The blood serum of such refractory animals gives no reaction of 

 fixation with cancer extract, and when injected simultaneously 

 with cancer in susceptible rats leads to no prevention of the growth 

 of the tumor. The refractory blood, however, when injected pre- 

 viously to or at the same time with the tumor in naturally insus- 

 ceptible rats gives a larger percentage of " takes " than in control 

 animals. 



If a tumor is removed during the " premetastatic " period a 

 second implanted tumor seldom grows. Subsequent to this period 

 a second implanted tumor does grow. 



When a primary growing tumor is left and a second implanted 

 during the premetastatic period, not only does the second tumor 

 fail to grow but the first tumor entirely disappears in many in- 

 stances. In cases in which the resorption of original tumor was 

 incomplete, from lack of sufficient time the primary tumor showed 

 regressive changes in the nature of cell degeneration or a marked- 

 increase of connective tissue stroma. 



A reaction of fixation was found with the blood of a few ani- 

 mals with tumor during the premetastatic period but never during 

 metastatic period. The premetastatic period then would seem to 

 be characterized by an active defence on the part of the animal 

 body and during this period reimplantation of tumor increases this 

 resistance to such an extent that the original tumor is destroyed. 

 When this period is passed metastases occur and a second im- 

 planted tumor grows. 



34 (372) 



Influence of temperature upon pepsin. 

 By A. 0. SHAKLEE. 



\^From the Laboratory of the Department of Physiology and Phar- 

 macology of the Rockefeller Institute for Medical Research^ 

 While studying the destruction of pepsin by shaking pepsin 



solutions it was thought essential to make some study of the spon- 



