690 STUDIES IN GENERAL 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 toa 
suppression or a reduction of the antagonistic process that 
shortens life. In the case of the egg of Cheetopterus 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 
Echinoderm 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.’ 
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 thedevelopmentof carcinoma may bea similar phenomenon. 
The catalytic substances which are givenoff by thecancer para- 
sitemay 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. 
1We 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. 
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