TO PHYSIOLOGY AND PATHOLOGY. 31 



BY THIS MEANS THEY BECOME THE ENEMIES OF THE PROCESS 



OF PUTREFATION. 



It can no longer be doubted tbat nature has assigned to the infusoria the im- 

 portant part of being the enemies and opponents of all contagion and miasma ; 

 since the most incontrovertible facts have shown that the green and red infusoria 

 are during their life, and the process of their propagation, sources of the purest 

 oxygen. 



In a similar manner fungi check putrefaction by converting to their own nutri- 

 ment, the sulphurous and nitrogenous constituents of vegetables the actual 

 originators of corruption; and thus- further, the general transition into the final 

 products of corruption. 



THE NATURE OF YEAST. 



The views which the adherents of the parasite theory have formed as to the 

 cause of putrefaction, mainly rest upon observations which have been made upon 

 the formation of the yeast in the fermentation of wine and beer ; but the investi- 

 gations into the nature of the yeast are not yet closed, and it is to be presumed 

 that the mocroscopic observations already made will be strengthened by further 

 inquiry, and every doubt concerning its vegetable nature be thus set aside ; yet 

 even in this case the explanation regarding the separation of sugar into alcohol and 

 carbonic acid, would admit of no other expression than that assumed by the 

 chemical theory. 



RELATION OF THE YEAST IN SOLUTIONS OF SUGAR, IN GRAPE 

 JUICE, AND BEER WORT. 



It is a perfectly well known fact that in spirituous fermentation, the elements of 

 the sugar of grapes without any loss of weight, and those of the sugar of cane 

 with an increase of weight, are given back in the form of carbonic acid and 

 alcohol. We cannot here, according to our usual conceptions, speak of the con- 

 version of the atoms of sugar to the nutritive and respiratory processes of an 

 organic being. The weight of the yeast increases in the fermentation of the juice 

 of the grape and beer-wort ; but if we put the yeast in a solution of pure sugar 

 and water, although the fermentation is equally produced, the yeast, in this case, 

 instead of gaining, loses a portion of its weight ; and by continuous contact of the 

 same yeast with fresh sugar and water, it by degrees entirely loses the power of 

 fermenting, while its weight constantly diminishes. In this case, as we see, one 

 and the same action must be derived from two directly opposite causes, to one of 

 which is ascribed the capacity for increase, and to the other the reverse of propa- 

 gation. If we a-ssume that the nutritive and re-spiratory processes of the fungi are 

 dependant upon sulphurous and nitrogenous substances contained in their elements, 

 and that the fermentation of sugar is an accidental phenomenon, accompanying 

 the developing process of an organic being, then it is quite incomprehensible whence 

 it arises that the fungi are not reproduced in a fluid, where there is present this 

 chief requirement to their propagation, while they gain in weight as soon as sugar, 

 the accidental attendant of this vital process, is added. If, for instance, in the 

 juice of the grape, sugar be decomposed, and there 'is no free access of air, the 

 remainder of the dissolved sulphurous and nitrogenous substances will remain 

 dissolved in the juice for years without undergoing any change ; if sugar be then 

 added, the fermentation begins again, and yeast is again separated ; when the sugar 



