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SCIENCE 



[N. S. Vol. XLIII. No. 1105 



living body, and that this reduction in the 

 quantity of body fluid is very much greater 

 than the reduction in the quantity of tissue. 

 Furthermore, in the body the fluid in eon- 

 tact with the tissue is constantly renewed 

 and the old fluid is eliminated. In vitro 

 the fluid remains relatively constant. 

 There exists also the possibility that the 

 action of the body fluid is a complex one in 

 vivo in a way similar to the complex action 

 after homoiotransplantation. In the case 

 of both types of substances (those pre- 

 formed and those produced through immu- 

 nization) , we are able to point to analogous 

 substances existing elsewhere, namely, the 

 preformed species-specific tissue coagulins, 

 which play a role in the blood coagulation, 

 and the secondarily, artificially produced 

 antibodies of various kinds. It also remains 

 further to be determined, how far the 

 metabolic products of foreign cells exert a 

 direct influence upon each other and how 

 much of this effect is dependent upon the 

 interaction between cells and foreign body 

 fluids. 



In addition to the effect of toxic sub- 

 stances, mere lack of common food-stuffs 

 can also retard tumor growth, as the re- 

 tarded growth of transplanted tumors in 

 pregnancy and the feeding experiments of 

 Moreschi, Peyton Rous, Beebe, Sweet, Cor- 

 son White, and Saxon, Robertson and Bur- 

 nett have shown. Other substances appar- 

 ently stimulate tumor growth (Robertson 

 and Burnett). Whether an immunity 

 caused through the lack of specific sub- 

 stances — in contradistinction to the com- 

 mon food Eind growth stuffs of cells — 

 whether, in other words, an athreptic im- 

 munity, as Ehrlich called it, exists, how- 

 ever, is very doubtful. Such an athreptic 

 immunity certainly would not explain the 

 phenomena referred to above, as especially 

 the experiments of Uhlenhuth, Haendel and 



Steffenhagen, Tyzzer and Levin have 

 shown. 



In the retarded cancer growth in preg- 

 nancy especially we do not have to deal 

 with a scarcity in specific growth sub- 

 stances, particularly in hormones, as Ehr- 

 lich supposed, but with a shortage in the 

 ordinary substances required for the build- 

 ing up of cells. On the contrary, it seems 

 to us very probable that certain hormones 

 which circulate during pregnancy may be 

 of advantage to tumor growth, and that 

 these two antagonistic factors — deficiency 

 in ordinary building material and presence 

 of special hormones — may preponderate un- 

 equally in different cases and thus the 

 difference in the effects on tumor growth 

 which certain investigators found in preg- 

 nancy may be explained. 



In connection with the studies in metab- 

 olism to which we have just referred, we 

 may look forward to interesting results 

 through further analysis of the chemical 

 constitution of tumor tissues. 



I am, however, inclined to regard the 

 differences so far found between normal 

 and tumor cells in a similar light, as differ- 

 ences observed in the case of mitotic divi- 

 sion in normal and tumor cells, both prob- 

 ably being the result and not the cause of 

 the changes in the growth energy character- 

 istic of tumor cells. 



Having arrived at the end of our survey, 

 we must confess that much remains still to 

 be done before these investigations can in 

 any way be considered near completion. 

 On the other hand, I believe that I have 

 indicated that there are yet other ways open 

 for further attack upon the problems of 

 cancer and tissue growth, and I hope also 

 that I have been able to convey the im- 

 pression that the work of so many investi- 

 gators in this field has not been in vain, and 

 that not only this special branch of sci- 

 ence has been built up, but that also biology 



