22 
Scientific Proceedings (40). 
14 (539) 
The influence of an inoculation with tumor material of experi- 
mentally decreased virulence upon the result of a 
second inoculation with tumor material of 
experimentally decreased virulence. 
By ELLEN P. CORSON WHITE and LEO LOEB. 
[From the Laboratory of Experimental Pathology of the University 
of Pennsylvania and from the Department of Pathology 
of the Barnard Free Skin and Cancer 
Hospital, St. Louis.] 
Eight years ago one of us has shown that through the influence 
of chemical and physical factors it is possible to decrease the 
energy of growth of tumor-cells without killing the cells. 1 While 
a certain degree of injury kills the cells, a graded decrease in the 
action of the external agency leads to corresponding gradations 
in the decrease in the energy of growth of the cells. Thus it is 
possible to obtain tumor material which is still alive, but which 
gives rise to a very insignificant growth in many instances, and 
the initial growth of which is in many cases followed by a spon- 
taneous retrogression. At that time we considered the possibility 
that such tumor material of experimentally decreased virulence 
might serve as a vaccine which might provide a certain protection 
against a second injection with more virulent material. 
We tested therefore the influence of a first injection of such 
material upon the growth of a subsequent inoculation with tumor 
material. In the majority of cases both inoculations were sepa- 
rated by an interval of 10-20 days. 
In order to obtain a more sensitive reagent indicating the 
presence of even a slight immunity, we used as material for the 
second (or sometimes third) test-injection not virulent tumor 
pieces, but again tumor material of experimentally (through 
heating) decreased energy of growth. Our results were as follows: 
1. If the tumor material of experimentally decreased virulence 
did not give rise to tumor formation, no immunity was noticeable, 
even if the mice had received two or three preparatory injections 
Wirchow's Archiv, Bd. 172, 1903, p. 395. 
