v.] IN THE THEORY OF NATURAL SELECTION. 32 1 



nervous diseases, viz. from motor paralysis, to a less degree 

 from sensory, and to a high degree from trophic paralysis ; in 

 rare cases, when the symptoms of paralysis are very marked, 

 epilepsy is also transmitted. 



If we now remember that a considerable number of diseases 

 are already known to be caused by the presence of living 

 organisms in the body, and that these diseases may be trans- 

 mitted from one organism to another in the form of germs, 

 ought we not to conclude from the above-mentioned facts, that 

 the symptoms are due to an unknown microbe which finds its 

 nutritive medium in the nervous tissues, rather than to suppose 

 that they are due to morphological changes, such as a modifica- 

 tion of the histological or molecular structure of certain parts of 

 the nervous system ? At all events, it would be more difficult 

 to understand the transmission of such a structural change, 

 than the passage of a bacillus into the sperm- or germ-cell of 

 the parent. There is no ascertained fact which supports the 

 former assumption, but it is very probable that the transmission 

 of syphilis, small-pox and tuberculosis ^ is to be explained b}^ 

 the latter method, although the bacilli have not yet been de- 

 tected in the reproductive cells. Furthermore, this method 

 of transmission has been rigidly proved in the case of the 

 muscardine disease of the silkworm. At all events we can 

 understand in this way how it happened that the offspring of 

 artificially epileptic guinea-pigs were affected with various 

 forms of nervous disease, a fact which would be quite unin- 

 telligible if we assume the occurrence of a true hereditary 

 transmission of a morphological character, such as a patho- 

 logical change in the structure of some nervous centre. 



The manner in which artificial epilepsy becomes manifest 

 after the operation, is also in favour of the explanation offered 

 above. In the first place epilepsy does not result from any one 

 single injury to the nervous system, but it may follow from a 

 variety of different injuries. Brown-Sequard produced it b}^ 

 removing a portion of the grey matter of the brain, and by 



^ A direct transmission of the germs of disease through the repro- 

 ductive cells has lately been rendered probable in the case of tuberculosis, 

 for the bacilli have been found in tubercles in the lungs of an eight-months' 

 foetal calf, the mother being affected at the time with acute tuberculosis. 

 How^ever it is not impossible that infection may have arisen through the 

 placenta. See ' Fortschritte der Medicin,' Bd. Ill, 1885, p. 198. 



