24 THE SPIRIT OF THE SOIL 



ditions of its atmosphere, of the laws governing its 

 movement through space, so there are many proper- 

 ties of the bacterium on which it is safe to dogmatize. 

 We know that the bacterium is an organism low in 

 the vital scale, consisting of a single cell, the proto- 

 plasm or vital unorganized portion of which is sur- 

 rounded by a cell membrane which may consist of 

 cellulose, but which more often is made up of a horn- 

 like substance. We are on sure ground when we 

 state that it usually reproduces its kind by forming 

 a partition in the middle of its substance and dividing 

 into two. Observation has taught us that the time 

 taken for division is in favourable conditions about 

 half an hour. It is certain that in the vast kingdom 

 of the bacteria there are only a few that are able to 

 give rise to diseases in man and animals. Most of 

 these have certain characteristics that enable them 

 to be certainly identified and incriminated by the 

 bacteriologist. The pathologist has gone farther, 

 and is getting an insight into the means by which 

 the body is able to repel the attacks by which it 

 is constantly threatened. He talks learnedly of 

 opsonins, antibodies, and the like, and his know- 

 ledge at any rate is sufficiently precise and accurate 

 to enable him to build up on it a rational system 

 of treatment for the individual struck down by a 

 disease. 



While the bacteriologist who has directed his 

 attention to the bacteria connected with the causa- 

 tion of disease stands on a firm foundation of proved 

 and demonstrated fact, and may compare his results 

 with those with which the astronomer deals in 



