4 INTRODUCTION 



intestinal tract in many Arctic animals the polar bear, 

 reindeer, seal, eider duck, etc. is generally sterile, and in 

 these instances, therefore, bacteria are not required for 

 normal nutrition. 



Commercially, micro-organisms are of the utmost 

 importance. Without them there would be no fermen- 

 tation, and the wine, beer, and indigo industries, the 

 ripening of cheese and tobacco, and many like processes 

 would be non-existent. From a financial aspect also 

 micro-organisms cannot be ignored, for many of the so- 

 called " diseases " of beer and wine, which often occasion 

 great loss, are due to the entrance of adventitious forms, 

 while the silk industry and sheep farming in France were 

 once threatened with extinction owing to the ravages of 

 pebrine and of anthrax respectively, but through the 

 genius of Pasteur were restored to their former prosperity. 

 There is no need to emphasise the importance of micro- 

 organisms frorn a medical and hygienic point of view, 

 but the fact may be recalled that sixty years ago the 

 mortality after operations was very high, and that 40 per 

 cent, of these deaths were caused by pyaemia, septicaemia, 

 and hospital gangrene, conditions which are due to the 

 entrance of micro-organisms, and which are now almost 

 preventable, thanks to the antiseptic system introduced 

 by Lord Lister. 



The theory of spontaneous generation or abiogenesis is 

 intimately connected with the study of bacteria. The 

 putrefaction of animal and vegetable fluids even after 

 boiling, and the growth in them of minute living forms, 

 were held by many to be a sure proof of the development 

 of life from inanimate matter, of the spontaneous genera- 

 tion of the living from the non-living. A succession of 

 investigators, however, showed (1) that if the fluids be 

 boiled sufficiently long, and be then sealed up so as to 

 prevent the access of air, they do not undergo putre- 



