304 HEREDITY AND DISEASE 



healthfulness which, in spite of all disease, still surges around 

 us. 



Let us look for a little at the more hopeful aspects of the 

 question : 



(i) As regards microbic diseases, a predisposition to which may 

 be inherited, the progress of hygiene and preventive medicine 

 tends increasingly to diminish the risks of infection or of fatal 

 infection. 



(2) There is some reason to believe that, in regard to some 

 microbic diseases, a relative constitutional immunity is in 

 process of evolution. 



(3) There is no scientific warrant for believing that acquired 

 diseases — i.e. those arising as modifications from without, to 

 which there is no specific predisposition — are as such trans- 

 missible. By liberating toxins and the like in the body, or by 

 depressing the general nutrition, acquired diseases may pre- 

 judicially affect the germ-cells, and therefore the offspring. But 

 this is more remediable than specific changes in the germ-plasm. 



Our view of the harm done by an ill-considered widespread 

 belief in the transmissibility of modificational or exogenous 

 diseases has been well expressed by one of the keenest workers 

 in the Public Health service : " The nightmare of the specific 

 inheritance of acquired diseases overloads the spontaneity of 

 life, paralyses the will, and hampers the preventive service in its 

 efforts to improve the environment. Weismannism exalts the 

 social inheritances, which, as the great organs of selection, consti- 

 tute the basis of preventive medicine" (W. Leslie Mackenzie). 



(4) In regard to constitutional diseases, it seems on the whole 

 that " the inheritance of predispositions to particular diseases " 

 is a more accurate description of the facts that the common 

 phrase, " the inheritance of disease." There is no doubt that 

 many predispositions to particular constitutional diseases are 

 inherited. What have we to set against thi c ? We must 

 recognise that every item in an inheritance requires an ap- 



