DISTRIBUTION AND HABITAT OF THE BACTERIA. 693 



infective agents ; and the same soil was supposed, per- 

 haps at a definite stage of dryness, to enable the infective 

 germs to be transported by currents of air. 



This view was undoubtedly completely justified by the 

 state of our knowledge at that time as to the nature of the 

 pathogenic agents. But since we are now able to set on 

 foot direct observation and experimental investigations 

 as to the mode of development and the conditions of 

 existence of the infective agents, we must subject our 

 former views as to the occurrence of infective diseases, 

 and more especially as to the influence of the soil on the 

 pathogenic bacteria, to revision and criticism. In fact 

 as to the behaviour of bacteria in the various media in 

 our surroundings many thorough investigations are 

 necessary, and we are far from seeing clearly the re- 

 lations between the soil and the pathogenic bacteria. 

 But in many directions the more recent bacteriological 

 investigations have given us valuable facts which compel 

 us to alter our former views. 



If we shortly summarise what we have learned during Results of 

 the last few years by direct observation and experiment 



as to the general behaviour of the most various kinds of jal investiga- 



tions of soil. 



bacteria in the soil, we obtain in the first place the 



unanimous result that, as a matter of fact, the bacterial 



life in the soil is extremely active, that the soil is evidently 



the chief reservoir for bacteria, into which the greatest part 



of all fluids containing bacteria, almost all refuse water, 



excreta, &c., pass, and on the surface of which the germs 



which have passed into the air are again in great part de- 



posited. Enormous numbers of bacteria have always been Richness of 



found in the soil by the most various observers. Infusions various kind* 



made from manured field and garden earth, even though of bacteria. 



diluted 100 times, still contain thousands of bacteria in 



every drop, and the ordinary soil of streets and courts also 



shows the presence of large numbers. Bacilli are present 



in much the largest numbers ; but in the most super- 



ficial layers and in moist ground there are also numerous 



forms of micrococci. Some species are markedly promi- 



nent, and are found in the most varied places and at the 



most various times in the soil, while they occur in other 



