378 ANIMAL BIOLOGY 



insanity is inherited in accordance with Mendel's law. 

 We should distinguish hereditary insanity from insanity 

 that may be the result of accident, disease, alcoholism 

 or severe shock, although in many cases these alleged 

 causes only serve to awaken a hereditary proclivity that 

 is not strong enough of itself to make the person insane. 

 Insanity is not inherited in so clear cut a manner as albin- 

 ism or eye color; what is transmitted is rather a nervous 

 condition that may manifest itself as insanity, epilepsy 

 or other nervous disorders. Insanity appears to behave 

 as a recessive or partially recessive character. Matings 

 of normal and insane frequently produce only normal 

 children, although if the normal partner came from insane 

 ancestry a part of the children would probably be insane. 

 When both parents are afflicted with hereditary insanity 

 all of the children may be expected to become insane or 

 have some severe nervous affliction. If both parents are 

 sane but of insane ancestry the expectation is that one- 

 fourth of the children will be afflicted. While there 

 may be no cases of insanity among the immediate relatives 

 of the afflicted person his insanity may nevertheless be 

 inherited from more remote ancestors. From what is 

 known of the inheritance of insanity it is clear that people 

 in whom insanity is an inherited trait should not marry and 

 incur the risk of transmitting this terrible malady to 

 their children. 



Several careful studies have shown that feebleminded- 

 ness, like insanity, is inherited as a Mendelian character. 

 Feeblemindedness is capable of being detected in early 

 years, before insanity usually manifests itself, and in 

 the majority of cases it is clear that it is an inherited 

 character, although it sometimes results -from sickness 

 or injury. A very interesting study of the inheritance of 

 feeblemindedness is contained in a little book by Goddard, 



