SOME POSSIBLE BEARINGS OF GENETICS ON PATHOLOGY 31 



chlorophyll bodies are known to divide and to be distributed to 

 the two daughter cells at each division independently of the nu- 

 clear division and of the maturation process in the egg. 



Why, then, it is asked, may not there be present in the cyto- 

 plasm of the cell other self-perpetuating bodies that are respon- 

 sible for certain kinds of inheritance? Why not go further and 

 ask, why, since the cytoplasm appears to be handed down from 

 cell to cell, may it not furnish also a different medium for in- 

 heritance of characters? Theoretically such an argument is logi- 

 cal. No student of Mendelism would I think deny such a possi- 

 bility. But, as a matter of fact, it is not going too far to say 

 that, at present, there is little evidence that such inheritance takes 

 place, except in a few special cases, like that of the chlorophyll 

 bodies. It is safe, I think, to say that if cytoplasmic inheritance 

 played any important role in heredity in the higher animals and 

 plants, we should expect, by now, to have found many cases of it. 

 None are known to us. 



Whether Mendel's laws of heredity apply to unicellular ani- 

 mals, to bacteria and to similar types, in which the mechanism 

 for this type of inheritance has not been shown to exist, can not 

 be affirmed or denied from the evidence at hand. 



There are at present three outstanding cases in the higher ani- 

 mals, in which an induced variation is said to be inherited after- 

 wards. These cases are of great interest to pathology. We can 

 not afford to pass them over. First, there is Brown-Sequard's 

 claim that injuries to the nerve cord or to the cervical or sciatic 

 nerves of guinea pigs produce effects that are transmitted. 



Second, there are the cases of the inherited effects caused by 

 alcohol in guinea pigs discovered by Stockard. 



Third, there is Guyer's evidence that an effect on the eye, 

 caused by foreign serum, is transmitted. 



Brown-Sequard's experiments have been repeated several 

 times; almost always with negative results. Today his claims 

 are practically forgotten. 



Stockard' s results with guinea pigs, unlike those of Brown - 

 Sequard, have been done under carefully controlled conditions. 



