TO PHYSIOLOGY AND PATHOLOGY. 33 



relations of fresh urine in order to perceive that in many of these animal substances 

 a constantly renewed afflux of oxygen is a requirement for their putrefaction ; that 

 on the exclusion of oxygen, the urea does not pass into carbonate of ammonia, 

 and that, enclosed in a vessel, these substances convert the oxygen into carbonic 

 acid, and that with the removal of the oxygen, the whole process is arrested, or, at 

 all events, changed. 



The adherents of the parasite theory assume, that by the passing contact of 

 sugar of grapes with the air, (without which fermentation could not begin,) the 

 germ of the yeast plant which are present everywhere in the air, find access to a 

 soil which affords them the necessary requirements for their fruitful development ; 

 but they do not explain the reason why the brewer is obliged to add yeast in order 

 to turn his wort to a state of fermentation ; and why these same germs, if they 

 really were in the air, should not develope themselves in a soil so congenial to 

 the requirements of their life and propagation. They entirely forget that the fer- 

 mentation of the sugar of grapes begins with a chemical action, that a measureable 

 quantity of oxygen is taken up from the air, that the juice becomes turbid and 

 discolored, and the fermentation only begins after the occurrence of a precipitate ; 

 they do not consider that fermentation diminishes instead of increasing with the 

 additional quantity of oxygen ; and that under certain conditions when the matter 

 capable of taking up oxygen has become insoluble, fermentation no longer goes on 

 in the juice.* 



Before all these relations have been thoroughly examined, it would be contrary 

 to all sober inquiry to consider the vital process of an animal or plant as the cause 

 of any process of fermentation or putrefaction ; and in all cases where the pre- 

 sence of organic beings is not to be shown on investigation in the contagion of a 

 miasmatic contagious disease, the hypothesis of these bodies having or taking any 

 share in the process of disease must be rejected as altogether unsound. 



TWO SIMULTANEOUSLY OCCURRING PHENOMENA ARE FREQUENTLY 

 HELD TO BE A CAUSE, AND ITS EFFECT. 



Another no less grave error in the mode of considering and deciding upon a 

 question, is to look upon different phenomena, which are effects of one and the 

 same cause, as mutually dependent upon each other, and regarding the description 

 of the one phenomena as an explanation or definition of the other. 



EXAMPLES. 



This is the case, for instance, with the explanation which is given of fever, of 

 crises, <fec. A few examples of similarly false combinations, which daily occur in 

 life, will best exhibit what is here alluded to. 



in contact with putrifying or decayed animal substances entered into no combination 

 with oxygen ; while at the ordinary temperature, pure hydrogen was easily condensed 

 under these circumstances. This deserves attention in an inquiry into the influence of 

 heated air upon the process of putrefaction. Possibly the decomposition of infusoria 

 and the germs of fungi may not be the only cause of the change in this process. 



* Two cubic centimeters of must, three millimeters thick and thirty millim. in dia- 

 meter, in contact with twenty cubic, centim. of oxygen do not pass into a state of 

 fermentation ; while a similar stratum without the addition of oxygen occasions a con- 

 siderable development of carbonic acid. De Saussure in the Jahrbuch fur Chernie, voL 



Ixiv. pp. 47 51. i 







3 



