418 150TAN1CAL BIOLOGY. 



Thus lactic term en tat iou soon comes to an end unless calcium carbou- 

 ateorsome similar substance be added, whicli lemoves the lactic acid 

 from the solution as fast as it is formed. 



The other point is that in all fermentations, besides what may be 

 termed the primary products of the process, other bodies are produced. 

 In the case of alcoholic fermentation the primary bodies are alcohol and 

 carbon dioxide ; the secondary, succinic acid and glycerine. Delpino 

 has suggested that these last are residual products derived from that 

 portion of the fermentable matter which is directly applied to the nutri- 

 tion of the protoplasm. 



Yeast, itself the organism which etfects the remarkable changes ou 

 which I have dwelt, is somewhat of a problem. It is clear that it is a 

 fungus, the germs of which must be ubiquitous in the atmosphere. It 

 is difficult to believe that the simple facts, whicli are all we know about 

 it, constitute its entire life-history. It is probably a transitory stage of 

 some more complicated organism. 



I can only briefly r*^fer to ])Utrefaction. This is a far more complex 

 l>rocess than that which I have traced iu the case of alcoholic fermenta- 

 tion. In that, nitrogen is absent, while it is an essential ingredient 

 in albuminoids, Mhich are the substances that undergo putrefactive 

 changes. But the general principles are the same. Here, too, mc owe to 

 Scjhwann the demonstration of the fact that the eflective agents in the 

 process are living organisms. If we put into aflask aputrescible liquid 

 such as broth, boil it for some time, and during the process of boiling 

 plug the mouth with some cotton -wool, we know that the broth will re- 

 main long unchanged, while if we remove the wool putrescence soon be- 

 gins. Tyndallhas shown that, if we conduct the experiment ou one of 

 the high ghuners of the Alps, the cotton-wool may be dispensed with. 

 We may infer then that the germs of the organisms which produce i)ut- 

 refaction arc abundant in the lower levels of the atmosphere and are 

 absent from the higher. They are wafted about by currents of air; but 

 they are not imj)onderable, and in still air they gradually subside. Dr. 

 Lodge has shown that air is rapidly cleared of suspended dust by an 

 electric discharge, and this no doubt affords a simple explanation of 

 the popular belief that thunderous weather is favorable to putrefac- 

 tive changes. 



Cohn believes that putrefaction is due to an organism called Bacter- 

 ium termo, which plays in it the same i)art that yeast does in fermenta- 

 tion. This is probably too simple a statement; but the general phenomena 

 are nevertheless similar. There is the same breaking down of complex 

 into simpler molecules; the same evolution of gas, especially carbon 

 dioxide; the same rise of temperature. Themoreor less stable products 

 of the process are infinitely more varied, and it is difficult, if not im- 

 possible, to say, in thepresent state of our knowledge, whether in most 

 cases they are the direct outcome of the i)utrefactive process, or resid- 

 ual i)roducts of the ]M()toplasmic activity of the organisms which in- 



