COMBATING PARASITIC BACTERIA. 195 



of described forms already runs far into the hun- 

 dreds, and we do not yet appear to be approach- 

 ing the end of them. They are everywhere in 

 Nature, and their numbers are vast beyond con- 

 ception. Their powers of multiplication are in- 

 conceivable, and their ability to produce profound 

 chemical changes is therefore unlimited. This 

 vast host of living beings thus constitutes a force 

 or series of forces of tremendous significance. 

 Most of the vast multitude we must regard as 

 our friends. Upon them the farmer is dependent 

 for the fertility of his soil and the possibility of 

 continued life in his crops. Upon them the 

 dairyman is dependent for his flavours. Upon 

 them important fermentative industries are de- 

 pendent, and their universal powers come into 

 action upon a commercial scale in many a place 

 where we have little thought of them in past 

 years. We must look upon them as agents ever 

 at work, by means of which the surface of Nature 

 is enabled to remain fresh and green. Their 

 power is fundamental, and their activities are 

 necessary for the continuance of life. A small 

 number of the vast host, a score or two of spe- 

 cies, unfortunately for us, find their most favour- 

 able living place in the human body, and thus 

 become human parasites. By their growth they 

 develop poisons and produce disease. This small 

 class of parasites are then decidedly our enemies. 

 But, taken all together, we must regard the bac- 

 teria as friends and allies. Without them we 

 should not have our epidemics, but without them 

 we should not exist. Without them it might be 

 that some individuals would live a little longer, if 

 indeed we could live at all. It is true that bac- 

 teria, by producing disease, once in a while cause 



