290 HEREDITY AND DISEASE 



(d) Pre-natal Influences resulting in Mutilations, Multipli- 

 cations, etc. — Recent embryological experiments have shown 

 incontestably that certain types of monstrosity can be readily 

 induced artificially by subjecting the developing ovum to shak- 

 ings, alterations of temperature, injections of various stuffs, 

 and so on ; and although the experiments relate mainly to birds, 

 amphibians, fishes, and lower animals, there is some evidence 

 that analogous factors may occasionally operate in mammals. 

 Thus, the pressure of amniotic strands may divide the rudiment 

 of a limb into two or may cause a mutilation. All such cases 

 are equivalent to accidents in after-life ; they are in no way ex- 

 pressions of the inheritance, and there is no evidence to show 

 that they have any effect upon the inheritance. 



" TheHapsburg lower lip or the large nose of Orleans is truly 

 an item in the inheritance, but the occasional absence of an arm 

 (due to a constriction of the rudiment by a strand of the amnion) 

 is an intra-uterine acquisition ; it is congenital, but it is not 

 inherited " (Martins, 1905, p. 14). 



It has sometimes been remarked that certain families show 

 a hereditary tendency to have wens (" small cystic or encysted 

 tumours ") on the head and upper parts of the body. The nature 

 of the growth, its inconstant position, and the time at which it 

 appears (usually about middle age) show that we should not 

 speak of the inheritance of a wen, but rather of the inheritance 

 of some skin-weakness. 



§ 8. Some Provisional Propositions 



I. Abnormal Peculiarities may find Expression in One Sex 

 only. — It is an interesting fact that an abnormal element in 

 the inheritance may find expression in the males only or in 

 the females only. If we could understand this we should be 

 nearer understanding what sex really means. 



Haemophilia or a tendency to bleeding is a heritable ab- 



