XIX 



contact is the abode of innumerable micro-organisms whose 

 presence is necessary to us. Many of the processes of everyday 

 life are intimately associated with their specific activities, and, 

 says Woodhead, "it is now proved, beyond all dispute, that 

 their presence is not merely accidental but is absolutely essential 

 to the carrying on of, one might almost say, the most common- 

 place operations." These bacteria are a vast army of chemists, 

 and they are employed by Dame Nature in the great work of 

 reducing dead organic matter and separating and releasing its 

 constituent parts in order that these may be employed in the 

 building up and support of new life. "This," says Trouessart, "is 

 at once the beginning and the termination of the endless chain 

 which sustains the equilibrium of nature, in which there is no 

 creation, no destruction. Plants draw their nourishment from 

 the soil and the air in the form of mineral solutions, and are 

 devoured by animals or other parasites ; animals are in their 

 turn devoured by microscopic plants or microbes, and return by 

 means of putrefaction to the condition of mineral salts, which 

 are distributed in the soil, and serve anew for the nutrition of 

 plants." 



The knowledge which has been acquired in recent times of 

 the life history of septic bacteria has not only been invaluable in 

 surgical operations, where it has been the means of saving 

 numbers of valuable lives, but it has led to the re-establishment 

 on a prosperous footing of great industries which were threatened 

 with destruction until Pasteur began his wonderful course of 

 investigation and discovery. Hundreds of scientists are now 

 engaged in the study of bacteria and their life history, and the 

 general result of their investigations has been to throw new light 

 into what was once more or less obscure, to enable them to deter- 

 mine with accuracy questions which were previously unintelligible, 

 and to clear the way to a more perfect understanding of the 

 methods by which effect is given to natural laws. 



The exact study of such questions can be carried on only by 

 specialists ; but may not ordinary observers gain much by 

 acquainting themselves with the results of their investigations ? 

 Few of us are acquainted with the science of astronomy, but 

 that does not prevent us from reading with delight the books 

 which astronomers have given to the world. In the same 



