PHYSICAL FORCES INVOLVED IN BIOLOGICAL ACTIVITIES 167 



m/ 1 5 Na 2 HPO 4 ) was determined at different intervals. After the read- 

 ings became constant there was a difference of 0.0005 volts between the 

 theoretical data and the results obtained. 



With the above facts in mind it becomes possible to enter upon a 

 more intelligent discussion of the methods involved. It has been stated 

 previously that most microbiological experiments, having for their 

 purpose the study of reaction upon microbial life, fall under the follow- 

 ing procedures: 



(a) Kisch's method. 



(b) Ordinary titration method. 



(c) Colorimetric method. 



It is well known that Kisch's method is a dilution method wherein a 

 certain number of gram molecules of an 'acid or alkali are diluted to a defi- 

 nite quantity for the purpose of ascertaining the influence of the reac- 

 tion upon the life of bacteria. There are two distinct ways to apply 

 Kisch's method, namely: (a) immersing the bacteria in different dilu- 

 tions of acids or alkalis in pure water for different periods of time by 

 means of silk threads or any other convenient agents, and then testing 

 their vitality; or (b) adding a known percentage of acids or alkalis 

 directly to the culture medium (usually solution). In either case the 

 results obtained by Kisch's method indicate neither the influence of 

 "true reaction" upon microbial life nor the influence of molecular 

 concentration, because, as Lingelheim has shown, different acids of 

 the same molecular concentration have varying influence upon micro- 

 organisms, and the degree of influence is parallel to the dissociation 

 constant of an acid or alkali. This is especially true in the case of 

 the second manner of application, (b) , where adsorption is caused by the 

 culture medium. 



The ordinary titration method is generally employed in adjusting 

 reaction of culture medium, and also to measure the amount of acid or 

 alkali produced in the course of physiological tests. This method is 

 inaccurate in the study of physiological liquids containing more or less 

 amphoteric substances and a comparatively small quantity of H or OH 

 ions. In other words, it is impossible to determine the " true reaction" 

 in such a liquid by this method. Fuller's and Schultz's methods of 

 adjusting the scale of reaction of culture media are scientifically con- 

 demned by the recent investigation of Clark, who showed the fallacies 

 of the titrimetric method. Again, the adsorption phenomenon caused 



