DISTRIBUTION AND HABITAT OF THE BACTERIA. 705 



further infection without and hefore coming in contact 

 with the soil. And further, the preservation of the 

 pathogenic bacteria is certainly not an exclusive property 

 of soil ; on the contrary, sufficient preservation can occur 

 in very various substrata, especially when the bacteria in 

 question can readily form spores, as in the case of the 

 anthrax bacilli, or are already spore-bearing when they 

 leave the body, as in the case of the typhoid bacilli. 

 Many kinds of soil may perhaps in this respect be of 

 more than average value, and the preservation of the 

 spores in them may be remarkably long and complete. 

 But there are always so many other possible modes of 

 distribution of the pathogenic bacteria that the action or 

 want of action of the soil in their preservation cannot in 

 very many cases exercise any marked influence on the 

 spread of the epidemic. 



A third question arises, in what way bacteria preserved 3. How do the 

 in the soil can spread to man, and whether a definite bacteria d 



condition of the soil, varying according to time and place, 

 Ms much influence on this spread ? The following man ? 

 modes of transport may come into play in the case of the 

 bacteria of the soil : 



1. Winds, which carry up the dust, and with it the winds. 

 bacteria, from the most superficial layers of the soil, and 

 transport them through the air. From what has been 



said above as to the organisms of the air and as to the 

 movement of bacteria within the soil, it is evident that 

 such a detachment of bacteria is only possible in com- 

 pletely dry soil, and only from the superficial layers, 

 which are converted into dust. A thoroughly moist soil 

 does not permit the detachment of bacteria, nor does a 

 soil which possesses a superficial dry layer, but the outer- 

 most surface of which is moistened from time to time by 

 slight rains. 



2. The ground water, and the water taken from it for Ground water. 

 drinking and other purposes. Where there is a thick 



layer of cultivated soil above the ground water this mode 

 of transport cannot come into play ; but where the ground 

 water is only separated by thin layers of loose soil from 

 the surface, and where it can ultimately reach the sur- 



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