HEREDITY 223 



The same may be said of many types of insanity. The discrimination be- 

 tween sane and insane in general is possible on a legalistic and practical basis, 

 however difficult decision in particular cases may be. A perfectly sharp 

 borderline in the scientific sense can hardly be drawn. 



But insanity presents another aspect, in that there are certain disorders 

 of the nervous system characterized by definite symptomatic behavior 

 which clearly define them without reference to their severity or, in other 

 words, whether the sufferer is incapacitated or not. The most widely 

 illustrative perhaps is the disease known as essential epilepsy. Those most 

 slightly affected may not only be not incapacitated but may be mentally 

 quite normal or unusually brilliant people. Those most severely affected 

 are or frequently become unquestionably insane. In its mildest forms or in 

 its most severe, the symptomatology is characteristic. The difficulties of 

 recognition in the mild cases are due to the fact that the slight symptoms 

 long pass unnoticed. This disease is inherited in many cases, and apparently 

 usually as a Alendelian recessive. There are indications of sex linkage in 

 some instances and it sometimes appears as a dominant. Multiple factors are 

 probably involved. Other forms of insanity equally well characterized 

 are recognized and some are probably inheritable. 



LONGEVITY 



It has been increasingly recognized of late that the length of life of the 

 individual is a measurable biological phenomenon, the analysis of which 

 might uncover very interesting facts. It is, of course, a common impression 

 that length of life is determined in considerable measure by inheritance. 

 Some families are thought to be notably long lived. That the condition 

 is counter-balanced by equally well-marked short lived families is possible 

 but this is in the nature of the case less easy to be sure about. When an 

 individual lives a long time we think naturally of his constitution as a 

 responsible factor and when his ancestry and immediate relatives also 

 survive, the constitutional factor becomes more and more apparent. But 

 when an individual dies young, the disease of which he died or the accident 

 of fate which carried him off is the impressive feature. Suffice to say that 

 observations on selected families of animals, fruit flies and guinea pigs 

 particularly, have shown that length of life whether short or long is a defi- 

 nite family characteristic and have given us some clues regarding its 

 hereditary transmission. 



Hypothetically if the human race were comprised exclusively of those 

 we know as long lived such diseases as tuberculosis and typhoid fever would 

 be unknown or would be recognized as disorders, disturbing but not es- 

 pecially dangerous to hfe. Whereas if the population were exclusively of 

 the short lived, cancer, arteriosclerosis and many other diseases would be 

 practically unknown. 



