734 MODE OF SPREAD OF INFECTIVE DISEASES. 



preserved state by clothes, dressings, furniture, or from 

 the surface of the body. 



Unequal re- Also among the so-called facultative parasites we find 

 of%h?facnTta- ver y varying degrees of resisting power, and this in- 

 tive parasites, fluences the mode of spread to a much greater degree 

 than the temporary saprophytic multiplication. Anthrax 

 spores show, for example, a very marked resisting power, 

 and hence can be carried by the most various objects, and 

 can act after a very long interval of time ; the spores of 

 the typhoid bacilli which are possibly present in large 

 numbers in the dejecta of the sick do not, it is true, 

 possess such great resisting power, but they can never- 

 theless retain their vitality for several months in various 

 substances, in fluids, and in the dry state ; the cholera 

 bacilli, on the other hand, as mentioned above (p. 444), 

 die in a few days under the conditions normally present 

 in our surroundings. 



Non-con- In the third group of the non-contagious facultative 



tafive 8 faCUl " parasites we must include the exciting agents of malaria, 

 parasites. which, however, are as yet completely unknown ; these 

 organisms possibly belong to the mycetozoa, and pro- 

 bably multiply in water which is rich in vegetable 

 materials, and especially on marshy ground, and are 

 carried when drying occurs into the air immediately 

 over the surface. 



For a long time it has been the fashion to employ the 



term non-contagious for all those infective diseases in 



the spread of which our surroundings play a distinct role, 



and in these cases for example, in malaria it has 



been assumed that the infective agents are transmitted. 



Pcttenkofer's not by the sick, but by the surroundings. This incor- 



typho^fever rec * y i ew as * tne sources of infection has even been 



and cholera applied to the obligatory parasites ; but it is the faculta- 



last group. tive parasites, more especially such as the exciting agents 



of typhoid fever and cholera, that have been designated 



by a large number of epidemiologists as non-contagious, 



and placed in the same category as malaria. 



Undoubted Apart, however, from undoubted practical experience 

 nessof typhoid ^ at cholera and typhoid fever are contagious, the view 



fever and -j us t referred to, and which is now held chiefly by Petten- 

 cholera. J 



