TRANSMISSION OF DISEASE 265 



§ 4. Can a Disease be transmitted ? 



This is not a gratuitous question. Perhaps it is best answered 

 in the negative ! 



" A disease," says Prof. Martius (1905, p. 14), " is not an 

 entity nor a character, but a process — an abnormal process 

 injurious to the organism, which is set a-going by a causa externa 

 and runs its course in some part of the body." The process 

 is not transmitted, but the potentiality of it is involved in some 

 peculiarity in the organisation of the germ-plasm. " In the 

 sense in which the word ' inherited ' is used by biology, there 

 are no inherited diseases." They may be a-going before the 

 offspring is born, but they are not as such inherited. 



As the authority quoted says, the objector will doubtless at 

 once bring forward the case of haemophilia, which is markedly 

 heritable. But haemophilia is not a disease. Does not the 

 subject get along fairly well until he receives a wound ? There 

 may be some weakness in the walls of his blood-vessels which 

 makes them peculiarly vulnerable, there may be some obscure 

 peculiarity in his blood which prevents it coagulating, so that 

 bleeding even from a slight wound may be very persistent. But 

 there is no disease, if we mean by disease an abnormal process. 

 What is inherited is a peculiarity of the vascular system ; or 

 perhaps we should put it negatively, and say that some part 

 of the normal inheritance (some "determinant," in Weismann's 

 phrase) is absent in those who show haemophilia. 



Some inborn peculiarity of the nervous system, originating as 

 a germinal variation, may under appropriate conditions of 

 stimulus or lack of stimulus manifest itself as a disease, such 

 as some forms of paralysis. Some inborn peculiarity of the 

 muscular system, originating as a germinal variation, may 

 under appropriate conditions of stimulus or lack of stimulus 

 manifest itself as a disease — such as progressive muscular 

 atrophy. Similarly, some inborn peculiarity of the alimentary 



