2 70 HEREDITY AND DISEASE 



on a priori grounds we should expect the reproductive organs 

 — apart as they are in some ways from the everyday Hfe — to 

 be affected by the widespread disturbance of nutritive meta- 

 bohsm, 



Weismann has suggested that the oscillations of nutrition 

 in the body prompt variations in the germ-plasm. Diseases may 

 cause profound changes in the nutritive stream, and those 

 particularly constant forms of whirlpool which we call the 

 germ-cells, which repeat themselves and propagate themselves, 

 generation after generation, age after age, may as the results 

 of bodily disease exhibit variations. Stable as the germ-plasm 

 must be supposed to be, we cannot conceive of it as an unrelated 

 entity. We believe that this interpretation covers many of the 

 cases which are called " inheritance of disease." 



It must also be remembered that while the chromatin of 

 the nucleus is almost certainly the real vehicle of the hereditary 

 qualities, the germ-cells also include some extra-nuclear 

 cytoplasm which may be affected in a general way by somatic 

 changes. The ovum, in particular, has a relatively large mass 

 of cytoplasm — its general cell-substance — which is the pre- 

 liminary building-material of the embryo. It is cutting it 

 too fine to say that what affects the cytoplasm of the egg is 

 not part of the inheritance, since that is really hidden in the 

 penetralia of the nucleus. The egg-cell is a unity, an individuality, 

 a miniature organism, and anything in it (except, of course, 

 another living creature — namely, a microbe) is at any rate a 

 close annexe of the hereditary vehicle in the nucleus. 



It is experimentally certain that germ-cells are markedly 

 susceptible to toxins of various kinds, such as alcohol, nicotin, 

 and hydrocyanic acid, and that abnormal developments result. 

 Therefore, since many diseases produce toxins in the body, 

 these may affect the germ-cells prejudicially, and thus there 

 may be an inheritance of the secondary effects of disease. 



What comes practically to the same thing for the individual 



