50 THE TREND OF THE RACE 



The first serious attempt to study the inheritance of insanity 

 in the light of Mendel's law was made by Cannon and Rosanoff 

 who carefully collected data from the families of n insane pa- 

 tients in the Kings Park State Hospital, New York. The authors 

 employed the method of sending out field workers to study the 

 families of the patients, and they were thus able to secure much 

 more reliable data than that which is usually collected by hospi- 

 tals and asylums. It was concluded that insanity behaves as a 

 Mendelian recessive character. The expectations of this hypoth- 

 esis that matings of insane with insane (RRXRR) would give 

 nothing but insane offspring is quite consistent with the results. 

 Out of three such matings yielding 16 offspring, 10 were neuro- 

 pathic, 5 died in infancy, and data concerning the remaining 

 one were wanting. 



The mating of normal persons heterozygous for neuropathic 

 defect, with neuropathies is represented, according to the authors, 

 "by 19 matings with a total of 129 offspring. Theoretically 

 one-half of these should be neuropathic, and one-half normal, 

 but capable of transmitting the neuropathic make-up to their 

 progeny. The charts show: 45 neuropathic, 14 normal with 

 neuropathic offspring, 20 normal without offspring, 27 normal 

 with normal offspring, 20 died in childhood, and concerning 3 

 data were uncertain." 



This is not a very close approximation to the Mendelian 

 expectation, under the assumption that we are dealing with 

 DRXRR matings. Upon what basis is one of the parents con- 

 sidered heterozygous for the neuropathic taint? Evidently the 

 authors have counted as heterozygous all those apparently nor- 

 mal persons who have produced neuropathic offspring when 

 mated with a neuropathic person. This procedure affords a 

 perfectly clear case of begging the question, for it assumes the 

 truth of the conclusions to be established, and entirely overlooks 

 the possibility previously pointed out, that the dominance of the 

 normal condition may be variable or imperfect. On the assump- 

 tion of Mendelian inheritance the only reliable index of the 

 heterozygous make-up of the normal parent is that one of the 



