DISTRIBUTION AND HABITAT OF THE BACTERIA. 699 



the pathogenic organisms, absolutely require a small 

 quantity of the best nutritive materials for their growth 

 and multiplication. In this respect the pathogenic bacteria 

 show a marked contrast to some of the saprophytic 

 forms, which can maintain life with nutritive materials 

 of almost any quality, and can, therefore, grow actively 

 in the soil. Better nutritive materials may, however, 

 be occasionally found in certain localities in the most 

 superficial layers of the soil, but at the most only tem- 

 porarily, because rapid destruction and decomposition 

 is always being brought about by saprophytic bacteria, 

 and by the surface action of the elements of the soil. 

 Various pathogenic bacteria can, it is true, be cultivated 

 in pure diluted urine, and Schrakamp has also observed 

 a development of anthrax bacilli in soil which was pre- 

 viously sterilised, and to which urine, blood serum, 

 nutritive jelly, &c., were added. From this, however, 

 we cannot draw any conclusions as to the conditions of 

 the normal soil. The excreta, &c., reach it usually Direct exp 

 in a markedly altered condition, and containing nume- ^gatlvl^'' 

 rous saprophytic bacteria. As a rule they become very resu lts. 

 much diluted in the soil by rain, and the layers in 

 which they are in the first place retained are likewise 

 full of saprophytes and fermentative agents, and in a 

 suitable state for rapid decomposition of the material. 

 Hence manured soil presents very different nutritive 

 conditions to those of pure fluids, and conclusions as to 

 the behaviour of the natural soil can only be drawn from 

 experiments with real manured field and garden earth. 

 Experiments of this kind have already been made by 

 Koch. He attempted to grow anthrax bacilli in garden 

 earth, in very rich mould from the banks of rivers, in 

 the mud of the same rivers, and also in the mud of 

 streets, a little water being added to these substances. 

 Nevertheless no growth occurred. Praussnitz has also 

 made investigations in this direction in the author's 

 laboratory, but has not as yet obtained any marked or 

 permanent multiplication of pathogenic bacteria in any 

 kind of soil, or by any mode of manuring. These ex- 

 periments are being continued, and it is very possible 



