388 THE GERM-PLASM 



nected with heredity, and many of them are in all probability 

 to be explained as the result of infection of the parental 

 germ-cell with microscopic parasites, and ought consequently 

 to be described as infections of the germ. 



In man such a transference of disease has only definitely 

 been proved to occur in the case of syphilis.* The father, as 

 well as the mother, is capable of transmitting this disease to the 

 embryo, and the only possible explanation of this fact is. there- 

 fore, that the specific bacteria of syphilis can be transmitted 

 by the spermatozoon. Amongst the lower animals the 'peb- 

 rine ' of the silkworm is an example, which has been well 

 known for several decades, of the transference of a fatal 

 disease from one generation to another through the egg : the 

 germs of the fungus which produces the disease penetrate into 

 the yolk. It is not known why these germs do not develop 

 and multiply within the egg, and thus destroy it, but this is, 

 however, the case. The fungi only begin to multiply in the 

 young caterpillar f when it is half- or full-grown, or the disease 

 may, again, only be fatal in the butterfly stage. 



As we now know that many diseases of man and other 

 mammals are due to such low forms of parasites, it is natural 

 to suppose that the transmission of such diseases results from 

 infection of the germ-cell with microbes, and not from inheri- 

 tance in the true sense of the word — that is, from the trans- 

 mission of an anomalous state of the germ-plasm itself. 



I have elsewhere attempted to trace the * heredity ' of ' epilepsy,' 

 produced artificially in guinea-pigs, by supposing that in this 

 case a similiar process occurs. The slow development of this 

 form of 'epilepsy,' resulting from an injury to the spinal cord 

 or one of the larger nerves, seems to me, indeed, to support the 

 conclusion that its symptoms, which resemble those of true 

 epilepsy, are due to the migration of microbes, which advance 

 from the injured part along the nerves in a centripetal direction 

 until they reach the brain, where they set up the state of irrita- 

 tion characteristic of the disease. The great inconstancy of 

 the symptoms, and the variety of forms of nervous diseases 

 which the offspring exhibit, also indicate that a true heredity is 



* C/., e.g., Dohrn, 'Zur Frage der hereditaren Infection,' Deutsche 

 med. Wochenschrift, Sept. 15, 1892. 



+ Cf., F. Haberlandt, ' Der Seidenspinner des Maulbeerbaums u. seine 

 Krankheiten W'ien, 1871. 



