THE BEGINNINGS OF LIFE. 391 



tative tendency. On the contrary, evidence has already 

 been adduced in this chapter to show that some acid solu- 

 tions are most prone to undergo evolutional changes of 

 a certain kind. These do not result in the production 

 of living things of a high type, but rather in an abund- 

 ance of organisms of a comparatively low type. It seems 

 to me, however, after careful observation and experi- 

 ment, that a neutral or slightly alkaline solution to which 

 a few drops of acid have been added is almost always 

 found, after a given time, to contain a notably smaller 

 number of organisms than an equal bulk of the unaltered 

 solution. And conversely, having an acid solution whose 

 productiveness is known, the number of organisms found 

 in equal bulks under similar conditions can almost 

 always be notably increased in either one of them by the 

 mere addition of a few drops of liquor potass*?., so as to 

 render it neutral or slightly alkaline. This, as previously 

 pointed out, may be interpreted as an indication that 

 alkalinity or neutrality of the fluids is more favourable 

 than their acidity for the occurrence of fermentative 

 changes. And thus the fact that organisms were never 

 met with when an acid c eau de levure sucree ' was used 

 in repeating the experiments of Schwann, though they 

 were met with, on the contrary, in other experiments 

 where portions of this same fluid had been used which 

 had been rendered slightly alkaline by the addition of 

 chalk, may be explained without the aid of that 

 supposition which alone seems to have occurred to 

 M. Pasteur. 



