REPR OD UCTION. 935 



that they are germinal from the first, is unwarranted. Direct experiments by 

 various investigators are almost as inconclusive. Weismann l has removed the 

 tails of white mice for five successive generations, and yet of 901 young every 

 individual was born with a tail normal in length and in other respects. Bos 2 

 has experimented similarly upon rats for ten generations without observing any 

 diminution of the tails. The practice of circumcision for centuries has resulted 

 in no reduction of the prepuce. The binding of the feet of Chinese girls has 

 not resulted in any congenital malformation of the Chinese foot. Brown- 

 S6quard, 3 and later Obersteiner, 4 have artificially produced epilepsy in guinea- 

 pigs by various operations upon the central nervous system and the peripheral 

 nerves, and the offspring of such parents have been epileptic. At first this 

 would seem to amount to proof of the actual hereditary transmission of mutila- 

 tions, yet in these cases the mutilation itself was not transmitted ; the offspring 

 were weak and sickly and exhibited a variety of abnormal nervous and nutri- 

 tional symptoms, among which was a tendency toward epileptiform convulsions, 

 the cause of which is still to be explained. Evidence from palaeontology 

 regarding the apparent gradual accumulation of the effects of use and disuse 

 throughout a long-continued animal series seems to require the assumption of 

 such a principle as the inheritance of acquired characters, but even here the 

 principle of natural selection may perhaps be equally explanatory. 



The Inheritance of Diseases. The question of the inheritance of diseases 

 has also been much discussed. The same general principles apply here as in 

 the inheritance of normal characteristics. The fact has been mentioned above 

 that pathological characters, whether anatomical, physiological, or psycholog- 

 ical, are capable of transmission. If, however, a pathological character has 

 been acquired by the parent and is not inherent in his own germ-cells, it 

 is extremely doubtful whether it can be passed on to the child. A diseased 

 parent, on the other hand, may produce offspring that are constitutionally 

 weak or that are even predisposed toward the parental disease, and such off- 

 spring may develop the parent's ailment. In such cases constitutional weakness 

 or predisposition, and not actual disease, is inherited ; the disease itself later 

 attacks the weak or predisposed body.' Proneness to mildness or severity of, 

 and immunity toward, certain diseases seem to be transmissible. These sub- 

 jects, however, are so little understood, and the real meaning of such terms as 

 predisposition, inherited constitutional weakness, and inherited immunity, is so 

 little known, that it is idle to discuss them here. 



Considerable experimental work has been performed recently upon the 

 transmissibility of infectious diseases. Undoubtedly infectious diseases cling 

 to a particular family for generations. The transmitted factor is probably fre- 

 quently, if not usually, simple predisposition. But in an increasing number 

 of cases there appears to be transmission of a specific micro-organism. Such 



I A. Weismann : Essays upon Heredity, vol. i., 1889, p. 432. 



II J. K. Bos : Biologisehes Cenlralblatt, xi., 1891, p. 734. 



s E. Brown-Se'quard : Researches on Epilepsy, etc., Boston, 1857 ; also various later papers. 

 4 H. Obersteiner : Mediziniscke Jahrbiicher, Wien, 1875, p. 179. 



