690 STUDIES IN GENEEAL PHYSIOLOGY 



partly antagonistic. They are both inhibited by a low tem- 

 perature, so that in this case death does not occur, although 

 no cell-division is possible. If we succeed in finding a sub- 

 stance which accelerates the process of cell-division at the 

 normal temperature, this will at the same time lead to a 

 suppression or a reduction of the antagonistic process that 

 shortens life. In the case of the egg of Chsetopterus a trace 

 of K ions acts as such a catalytic substance; possibly a trace 

 of H ions; and perhaps certain substances that are formed 

 when the egg loses a certain amount of water. For the 

 Echiiioderm egg we know at present only the last factor. In 

 addition there are the catalytic substances carried or pro- 

 duced by the spermatozoon (ions? enzymes?). But there are 

 certainly other catalytic substances, as is proved by tumors 

 and galls, in which the variety of structures corresponds to 

 an almost equal variety of parasites. 1 



It is very important to realize that the introduction of 

 catalytic substances into the egg does not prolong its life 

 unless the egg has reached a critical point determined by 

 two sets of conditions. The one is the maturity of the egg, 

 the other the change of conditions connected with the egg 

 leaving the ovary. As long as the egg is immature it lives 

 without the introduction of these substances or the sperma- 

 tozoon, and this may be true for the mature egg as long as 

 it remains in the ovary. The fact that there is an age limit 

 for the development of carcinoma may be a similar phenomenon. 

 The catalytic substances which are given off by the cancer para- 

 site may not be able to bring about cell-division in the epithelial 

 cells unless the latter have reached a critical point, which is 

 at least partly determined by the age of the individual. 



1 We do not need to assume a specific parasite for each kind of tumor. Tera- 

 tomas may be explained on the basis of the parthenogenetic tendency of the 

 mammalian egg in connection with some chemical change that furnishes the 

 catalytic substance. But it is not impossible that even in benign tumors, such as a 

 teratoma, the catalytic substance may be due to parasitic organisms. 



