710 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



Frequent dis- important mode of spread, more especially of such patho- 

 the typhoid genie bacteria as reach the soil directly or in a round- 

 thesoil fr m a ^ out wa J along with the dejecta of the sick (e.g., 

 typhoid bacilli), and which either contain resistant spore 

 forms in the dejecta as passed, or form these in the soil, 

 is that in one or other of the ways mentioned they are 

 again carried into the household from the uppermost 

 layers of the soil. And this distribution only occurs 

 from a porous soil, and at a time when a dry zone exists 

 (in other words when the level of the ground water is 

 low), that is to say, it depends markedly on local and 

 seasonal predisposition. 



Their distri- But even * ne typhoid bacilli are not always restricted 

 Imtion, to this mode of spread. We must assume that they 



however, does * 



not occur only can cause infection in other ways, and this assumption 



the'soS.? 8 is still more necessary in the case of those pathogenic 



bacteria which do not reach the soil to the same extent, 



or which (like the cholera bacilli) cannot be distributed 



from the soil in the most common manner, viz., by 



currents of air, for the reason that they cannot with- 



. stand the necessary degree of drying. In the case of 



the majority of the facultative parasites, therefore, their 



preservation in and distribution from the soil forms in 



reality a rare exception. 



The patho- The important difference between our views and those 



do n not a f c e quire of Pettenkofer is, therefore, that we (basing our opinions 

 infective on our present knowledge of the biology of the patho - 

 the result of genie bacteria and their behaviour in the soil) can find 

 6 soil! 06 nothing in the soil which must of necessity act on the 

 pathogenic bacteria in order to make them capable of 

 producing infection. The idea formerly held as to a 

 sort of ripening of the infective agents under the 

 influence of certain mysterious properties of the 

 soil cannot be brought into accord with the recently 

 ascertained facts as to the biological properties of the 

 bacteria, and must now be definitely abandoned. Nor 

 can we assume that the multiplication of pathogenic 

 bacteria takes place exclusively in the soil (perhaps with 

 the exception of the as yet completely unknown cause of 

 malaria) , because other superficial substrata are as a whole 



