HISTORY OF BACTERIOLOGY 3 



however, prevented him from recognising the true nature 

 of these organisms. 



Cohn a few years later shed fresh light upon the subject 

 by showing that the bacteria are plant-cells, with which 

 they agree in way of growth as well as in structure. In 

 1837 the important discovery was made by Schwann that 

 the phenomenon of alcoholic fermentation was connected 

 with the presence and life of the yeast-plant, and that 

 putrefaction was due * to something in the air which heat 

 was able to destroy.' These conclusions, although not ac- 

 cepted at the time, have subsequently proved to be correct. 



Henle in 1840 came to the conclusion that the cause of all 

 contagious diseases must be of a living nature, and further- 

 more he pointed out the necessary steps in a demonstration 

 of the casual connection between organisms and disease. 



The theory which was so long sustained by the authority 

 of the great chemist Liebig, that all fermentative and 

 putrefactive changes were due to purely chemical changes, 

 and that all albuminoid bodies, if left to themselves, would 

 sooner or later ^decompose spontaneously, owing to their 

 unstable chemical equilibrium, was responsible for the slow 

 progress of bacteriology during the next few years. 



Messrs. Schroder and Dusch in 1854 introduced the use 

 of cotton-wool for filtering air to free it from micro-organ- 

 isms, and for plugging apparatus. This apparently small 

 discovery did much for the forwarding of bacteriological 

 research. It remained for Pasteur to make the greatest 

 advance in the study of micro-organisms by making pure 

 cultures of various organisms, thus rendering an accurate 

 study of them for the first time possible. 



Pasteur'3 first experiments were devoted to the study of 

 -the yeasts, and the part they play in the phenomena of 

 fermentation. As Pasteur's classical experiments laid the 

 ioundations of the modern study of bacteriology, it may be 



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