io6 Lectures on Bacteria. [ ix. 



putrefaction. Cohn expresses this opinion in the most decided 

 manner when he says that he has arrived at the conviction, that 

 Bacterium Termo is the ferment of putrefaction in the same 

 sense as beer-yeast is the ferment of alcoholic fermentation, that 

 no putrefaction begins without B. Termo, or proceeds without 

 its multiplication, and that B. Termo is the primary exciting 

 cause of putrefaction, the true saprogenous ferment. Although 

 we cannot now maintain these propositions in their full extent, 

 and although the expression putrefaction is employed in them 

 without any precise determination of the processes of decom- 

 position and of the putrefying substance, yet on the one hand 

 there can be no doubt that the expression includes what is 

 commonly understood by the putrefaction of proteids, such 

 as meat, and on the other hand Bacterium Termo must, 

 at least, be a very constant attendant of such processes. It is 

 advisable, therefore, just to enquire what B. Termo actually is, 

 all the more since modern bacteriology itself scarcely ever uses 

 this old name. There is some ground for this, since it is 

 scarcely possible to make out with certainty what it was that 

 Dujardin, Ehrenberg, and others thirty years ago intended by 

 this name. What Cohn on the contrary described as B. Termo 

 in 1872 is an object as distinct as it is of frequent occurrence. 

 It is obtained by allowing the seeds, for instance, of leguminous 

 plants to rot in water, and then preparing a culture by introduc- 

 ing a drop of the putrid liquid into the solution known as 

 Cohn's nutrient solution for Bacteria 1 . The transference of a 

 drop of the solution thus infected several times in succession to 

 some fresh solution, sufficiently secures the purity of the culture. 

 The microscopic indication of the presence of Bacterium Termo 

 consists in the solution becoming more and more milky during 

 the first days of the culture, and then forming a greenish layer 

 on the surface, in which the form in question is collected in 



1 Cohn's normal solution, as given by Eidam in Cohn's Beitr. i. 3, 

 p. 210, consists of potassium phosphate I gr., magnesium sulphate I gr., 

 neutral ammonium tartrate 2 gr., potassium chloride o-i gr., water, 200 gr. 



