178 PROFESSOR LISTER. 



accoucheur. I allude to the changes in organic substances which 

 are designated by the general ievm /erme?Uation. 



In medicine, the large class of diseases termed zymotic derive 

 their name from the hypothesis that their essential nature is 

 fermentative. In obstetrics, puerperal fever, the most frequent 

 cause of disaster after childbirth, is now regarded by many of the 

 highest authorities as likewise due to fermentative disorder; and, 

 in surgery, among the various causes which may disturb a wound, 

 we know that by far the most frequent in operation, and the 

 most pernicious in its effects, both upon the wounded part and 

 upon the constitution, is putrefactive fermentation. If this be 

 so, it is clear that to understand the nature of fermentation must 

 be a matter of the very highest importance, with a view to curing 

 or preventing the various evils to which I have alluded. 



AYhat, then, do we mean by fermentation? I shall best 

 approach the answer to this question by giving an example. 

 Bather more than a week ago, I witnessed in the north of Italy 

 the time-honoured practice of treading grapes in the wine-Tat. 

 I was told that the juice would within twenty-four hours boil, as 

 it was said, over the vats into which it was introduced ; in other 

 words, that the sugar of the grape-juice would within that short 

 lime be so converted into alcohol and carbonic acid that the 

 carbonic acid gas, by its evolution, would cause sufficient froth- 

 ing to produce the effect to which I have referred. This conver- 

 sion of the sugar of the grape into alcohol and carbonic acid is ac- 

 companied by the development of a microscopic organism, the 

 yeast-plant, or, to continue the old nomenclature. Tornla cerevisicB, 

 consisting of microscopic cells multiplying by pullulation, as indi- 

 cated in this diagram (not here represented). Now, it is, I believe, 

 universally admitted that the alcoholic fermentation of grape-sugar 

 is due to the growth of the yeast-plant. M. Pasteur thinks that 

 he has traced the origin of the yeast-plant in the juice of the 

 grape to a minute fungus adhering to the outside of the skin of 

 the grape.i Be this as it may, it is admitted on all hands that 

 the alcoholic fermentation is caused by the growth of the yeast- 

 plant. So long as the juice of the grape is protected by the skin 

 of the berry, no fermentation occurs ; but, as soon as it escapes 

 from that protection, the organism, by its development, induces 

 the fermentation. Nor is it by any means exclusively in the 

 natural juices of fruits that such fermentation occurs. Any 

 sugary solution, provided it contains, besides the sugar, other in- 

 gredients requisite for the nutrition of the yeast-plant, will serve 

 as pabulum for the organism, and in that case the yeast-plant 

 will give rise to the fermentation, Here is a glass containing 

 what is termed Pasteur's solution, a solution devised by M. 

 ' Vide Pasteur, ' Etudes sur la Biere,' pp. 150 ei seq. 



