342 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the spermatozoa of their own species ; while the acid sea water in which 

 the eggs were treated will, when filtered and neutralized with X;iOH, 



induce a very powerful cluster formation. If it is true that the acid 

 dissolves the chorion or jelly-like substance surrounding the egg, the 

 experiment would prove that the substance which causes the cluster 

 formation is not formed in the egg but in the chorion. If this substance 

 is identical with the substance which Lillie calls " I. -rti 1 izin," his theory 

 concerning the role of this substance encounters serious difficulties. 



Eggs which have been treated with a mineral acid like HC1, and 

 have permanently lost the power of causing a cluster formation of the 

 spermatozoa, can nevertheless be fertilized normally with sperm of the 

 same species. "When the acid used was a fatty acid, and when membrane 

 formation occurred, the eggs also lost permanently their power of 

 inducing cluster formation, but retained their power of being fertilized 

 by sperm, provided that the membrane was first torn. The supernatant 

 sea water of the eggs of Strongylocentrotus franciscanus will not induce 

 cluster formation of the sperm of S. purpuratus, yet the sperm of the 

 latter will fertilize the eggs of the former. The sperm of Asterias 

 ochracea undergoes no cluster formation in the supernatant sea water 

 of S. purpuratus, no matter whether the sea water is normal or hyper- 

 alkaline, but the starfish sperm readily fertilizes most or all of the eggs 

 of S. purpuratus in hyperalkaline sea water. Loeb concludes that the 

 facts mentioned in this paragraph prove that the substance which is 

 responsible for the cluster formation is not necessary for the process of 

 fertilization. 



Germ Cells and Somatic Cells.* — Leo Loeb discusses the relation 

 between germ cells and somatic cells in the light of some results of 

 experimental pathology. 



1. Investigation of tumour growths (cancer) has brought to light 

 facts which are against the conception of a radical difference between 

 germ cells and somatic cells, as far as potential immortality is concerned. 

 As is most clearly seen in superficial cancers, the cancer cells are un- 

 doubtedly the offspring of ordinary somatic cells. In the case of 

 teratomata, the origin is probably from parthenogenetically developing 

 ova in the gonads or elsewhere, but the tumour cells are no longer germ 

 cells, but somatic cells. Now, one of the most characteristic properties 

 of cancer cells is that some kinds can grow after transplantation into 

 other animals of the same species. (Others are too sensitive apparently 

 to the chemical composition of the body fluids to survive transplanting.) 

 In each animal there are many successive generations of tumour cells, 

 and after transplantation each surviving cancer cell produces again new 

 generations. The potential proliferative capacity of the cancer cells is 

 enormous, and there is a great potential duration of life. An epithelial 

 tumour found by Jensen in a mouse has been propagated for almost 

 fifteen years. Tins suggests a potential immortality such as germ cells 

 and Protozoa have. Minot suggested that cytomorphosis (relative 

 increase in size and differentiation) implied death of somatic cells, but 



* Amer. Naturalist, xlix. (1915) pp. 236-305. 



