58 INFECTION AND IMMUNITY. 



ceps; the former occurrence of contagious hospital 

 gangrene through contamination of dressings and 

 of other infections from patient to patient through 

 unclean instruments or hands; these are examples 

 of conveyance by indirect contact. 



As some of them show, diseases which are ha- 

 bitually transmitted through the air (scarlet fever) 

 or by water (typhoid, cholera) may also be trans- 

 ferred by indirect contact. 



Hereditary In the strict zoological sense no form of trans- 

 ns fon" mission of an infection from parent to offspring 

 can be viewed as truly hereditary, since inheritance 

 concerns only properties which are inherent in the 

 germ cells and their chromatin. Micro-organisms 

 are foreign and their introduction in the germ 

 cells from the parent can only be considered as 

 accidental. It is, then, only for the sake of con- 

 venience and for lack of a more exact term that 

 the inheritance of infections is spoken of. This 

 distinction has been strongly emphasized by Han- 

 sen (Virch. Arch., Vol. 120) and by Lubarsch 

 (Ibid., Vol. 124:). Some of the metabolic diseases 

 and functional derangements, on the other hand, 

 may be truly inherited, or, perhaps better, a ten- 

 dency or predisposition to them may be inherited. 

 Also, it is very probable that susceptibility, or, on 

 the other hand, resistance to some particular infec- 

 tion, may be inherited, thus * accounting for the 

 frequent or rare occurrence of some infections in 

 a given family. 



Germ Ceii When disease of the offspring can be referred to 



>n ' a primary invasion of the germ cells (ovum or 



sperm cells) by micro-organisms it is said to have 



originated by "germ cell infection." It is not 



definitely known that this type of hereditary trans- 



