THE CAUSE OF INFECTIOUS DISEASE. 267 



human beings are rendered more easily suscep- 

 tible to infection than when in a sound and 

 normal condition. Before the days of anti- 

 septics the " healthy skin " played an impor- 

 tant part in the progress of a wound. 



The " specific " qualities of disease germs, 

 qualities which they possess as do all living 

 things adapted or adapting themselves to def- 

 inite conditions of life, can only become mani- 

 fest in the shape of a specific infectious disease 

 when the forms of motion which they impart 

 in order to overcome the resistances arising 

 from the organization of the human body hap- 

 pen to accord with the possibilities of motion 

 which occur in the structure of man as the re- 

 sult of inheritance and adaptation. Only in 

 this way is it possible to account for the fact 

 that as has been proved concerning some 

 moulds micro-organisms which, so far as we 

 know, occur only as saprophytes upon dead 

 material are able to produce disease when for 

 the first time, thus excluding any possibility 

 of an adaptation, they are artificially inoc- 

 ulated into susceptible animals. 



If the facts are considered in a scientific spirit, 

 rigorously and without prepossession, it is seen 

 that the sum of the qualities of a disease germ 

 is only apparently the " essence " of an infec- 

 tious disease, that in reality, here as elsewhere, 



