3101; E OF SPREAD OF INIECTIYE DISEASES. 



and cholera bacilli is of little importance, and lias but 

 little influence on the mode of spread of the disease, 

 while on the other hand it plays a more important role 

 in tropical countries. 



Local and The chief fact which Pettenkofer has brought for- 



disposition' 10 ward in support of his views is the peculiar local and 



may be ex- seasonal distribution of cholera and typhoid fever, which 

 plained with- , . , ,, 



out assuming according to him can only be explained as a result ot 



Influence 1 of some influence of the soil. It has been already shown 

 the soil. j n the chapter on cholera, and will be further discussed 

 below, that such local and seasonal variations in the 

 distribution of these diseases can be very well explained, 

 even though we hold to the opinion of the contagious- 

 ness of both diseases, and only ascribe to the soil the 

 role of a part of our surroundings, in that like other 

 substrata it harbours the infective agents given off by 

 the sick for a considerable time, and then again brings 

 them into contact with man. 



In accordance Having thus arrived at definite views as to the 

 sotVviewswe various modes of spread of the infective diseases, it is 

 have to con- easy ^ group together and characterise the sources of 



Rider the > . . . 



following infection in the case of each individual disease, ihe 

 following is the result in the case of the more impor- 

 tant infective diseases, omitting those whose mode of 

 transmission is as yet too imperfectly known (viz., 

 leprosy, recurrent fever, dysentery, yellow fever, &c.) : 



a. Contagious Obligatory Parasites. 

 (a) With slight resisting power. 



Syphilis and gonorrhoea : sources of infection, the 

 fresh secretions. 



Rabies : fresh saliva, blood, spinal cord, and brain. 



