1876.] Physico- Chemical Theory of Fermentation, ^c. 155 



single drop of it would suffice to infect man}" ounces, a gallon, or more 

 of the sterilized fluid. This, however, is nr,ver the case ; it only 

 fertilizes the barren urine when it is added in a proportion dependent 

 upon the ])recise acidity and quantity of the fluid with which experiment 

 is being made- 



2iid Hyi^o thesis. Tlie fertilizing agent may act hy reviving germs hitlierto 

 presumed to have been 'killed in the hoiled acid urine. — The acceptance of 

 this hypothesis would involve a general recantation of the previously 

 received conclusion that Bacteria and their germs are killed by boiling 

 them in acid fluids. But such a recantation would be scarcely justifiable 

 or acceptable unless based upon good independent evidence. 



The possibility, however, of accepting this second hypothesis is still 

 further closed by the results of experiments in which a slight excess 

 of liquor potassae was added to the boiled urine. Such fluids invariably 

 remained barren. Yet it can be easily shown that the mere develop- 

 ment and growth of Bactetna-gevms may take place both quickly and 

 freely in boiled urine containing a very large excess of liquor potassae *. 

 It would seem that this agent mixed v^dth boiled urine in quantity 

 slightly more than is needed for neutralization, prevents the origination 

 of living matter therein, although even when in considerable excess the 

 same agent affords no obstacle to the development, growth, and multi- 

 plication of germs purposely added thereto. 



In the face of these facts it would seem impossible to accept this 

 second hypothesis, even if it had not been independently negatived by 

 the great mass of evidence (lately reinforced by the experiments of 

 Professor Tyndall) to the effect that Bacteria and their germs are really 

 killed in fluids raised for a few minutes to the boiling-point (212^ F.). 



3rd Hypothesis. The fertilizing agent acts hy helping to initiate chemical 

 clianges of a fermentative character in a fluid devoid of living organisms or 

 living germs. — If the cause of the fermentation of the fluids in question 

 does not exist in the form of living organisms or germs either in the 

 fertilizing agent itself or in the medium fertilized, then it must be found 

 in some chemical reactions set up between the boiled liquor potassae and 

 the boiled urine. 



The experiments in which liquor potassae is added to urine in definite 

 proportions before and after it has been boiled with the result of inducing 

 fermentation in the otherwise barren fluids, as well as those in which 

 unaltered urine ferments under the influence of the high generating 

 temperature of 122° E. (50° C), all alike, therefore, point to the same 

 conclusion. They show, as other experiments have done, that an excJ usive 

 germ-theory of fermentation is untenable ; and they further show that 



A mixture of one part of liquor potassre to seven of boiled urine poured into a 

 bottle which has been washed with ordinary tap-water will, within forty-eigbt hours, 

 swarm with Bacteria if it is kept at a temperature of 122^ F. 



M 2 



