4 APPLIED BACTERIOLOGY 



liquid containing the organism that is desired to be grown 

 is largely diluted with sterile nutrient fluid favourable to 

 its growth. Drops of this diluted culture are then in- 

 oculated into separate test-tubes containing nutrient fluid. 

 By the extension of this process pure cultures are eventu- 

 ally obtained. It is of interest to note that Pasteur's first 

 experiments, which have led to such far-reaching results, 

 were made to disprove the spontaneous generation theory. 



The great controversy which started during the latter 

 part of the last century in connection with this subject 

 was briefly as follows : Those on one side regarded bacteria 

 as produced from organic matter by the process of putre- 

 faction, while those on the other hand believed they were 

 derived from living germs already present. The first 

 theory is that of ' abiogenesis,' or 'spontaneous genera- 

 tion'; the second that of 'biogenesis,' or 'life from life.' 

 The supporters of the former theory made the mistake of 

 supposing that all forms of life were destroyed by simple 

 boiling ; but, on the other hand, the Abbe Spallanzani, as 

 early as 1777, showed that once boiling was not sufficient 

 to destroy all living germs, but that repeated and pro- 

 longed boiling, care being taken to keep out aerial germs, 

 will entirely prevent meat-broth, etc., from undergoing 

 putrefactive changes. In spite of this, however, the dis- 

 cussion was continued for many years, until Pasteur, 

 Tyndall, and others, demonstrated that all putrefaction is 

 due to the action of bacteria, and that meat-infusion, milk, 

 wine, and other putrescible bodies, will keep indefinitely, if 

 due care be taken to protect them from germs after proper 

 sterilisation. 



If the ' abiogenesis ' theory were correct, it would be use- 

 less to fight against harmful bacteria, as these would again 

 and again be generated afresh. Fortunately, however, the 

 truth is found in the contrary view, that bacteria only 



