4 BACTERIA 



ditions of the infusions were natural, except that in the air 

 above them there was no dust. 



The sum-total of result arising from all these investigations 

 was to the effect that no spontaneous generation was possible, 

 that the atmosphere contained unseen germs of life, that the 

 smallest of organisms responded to the law of gravitation and 

 adhered to moist surfaces, and that micro-organisms were in 

 some way or other the cause of putrefaction. 



The final refutation of the hypothesis of spontaneous 

 generation was followed by an awakened interest in the 

 unseen world of micro-organic life. Investigations into 

 fermentation and putrefaction followed each other rapidly, 

 and in 1863 Davaine claimed that Pollender's bacillus of 

 anthrax, which was found in the blood and body tissues of 

 animals dead of anthrax, was the cause of that disease. From 

 that time to this in every department of biology bacteria have 

 been increasingly found to play an important part. They 

 cause changes in milk, and flavour butter ; they decompose 

 animal matter, yet build up the broken-down elements into 

 compounds suitable for use in nature's economy; they assist 

 in the fixation of free nitrogen ; they purify sewage ; in 

 certain well-established cases they are the cause of specific 

 disease, and in many other cases they are the likely cause. 

 No doubt the disposal of spontaneous generation did much 

 to arouse interest in this branch of science. Yet it must 

 not be forgotten that the advance of the microscope and 

 bacteriological method and technique have played a large 

 share in this development. The sterilisation of culture fluids 

 by heat, the use of aniline dyes as staining agents, the intro- 

 duction of solid culture media (like gelatine and agar), and 

 Koch's *' plate" method have all contributed not a little to 

 the enormous strides of bacteriology. Owing to its relation 

 to disease, physicians have entered keenly into the arena of 

 bacteriological research. Hence, from a variety of causes, it 

 has come about that the advance has been phenomenal. 



