1 68 PHYSIOLOGY OF MICROORGANISMS 



by the amphoteric substance in the course of titration is well known, 

 and, in the case of albumin, is usually expressed in the following 

 manner: 



i 



In acid solution H. albumin. OH = H albumin + OH 



+ 

 In alkali solution H. albumin. OH = Albumin OH + H 



The correctness of the above statement has been experimentally 

 demonstrated by Sorensen, Clark and others. 



In many cases the colorimetric method gives fairly accurate results, 

 but it has been noted that the presence of neutral salts as well as ampho- 

 teric substances interfere with the determination. It may, however, be 

 employed successfully if it is standardized for the particular liquid. 

 Lately Clark and Lubs employed the principle of the colorimetric method 

 for the differentiation of the colon-aerogenes family, using suitable 

 indicators. They have based their experiment upon the wide diver- 

 gence of the hydrogen ion concentration in a culture of one group and 

 of the other, and distinguished this difference by means of paranitro- 

 phenol or methyl red. The use of this method for physiologic work 

 other than for microbiology has been practiced by many. Sorensen 

 and Palitzsch determined the hydrogen ion concentration of sea water. 

 Henderson and Palmer used it in determining the acidity of urine to 

 diagnose normal and abnormal conditions. In any case, the colori- 

 metric method should be standardized previous to its use, by means of 

 the hydrogen electrode. 



Examining these methods critically in the light of physical chemistry 

 they are not satisfactory for the purpose of ascertaining the influence of 

 the so-called " true-reaction " upon microbial life. The hydrogen 

 electrode was devised to determine the hydrogen ion concentration, 

 and it has been used successfully in biologic fields. 



SURFACE TENSION 



Due to such forces as cohesion and adhesion the particles of bodies 

 have a tendency to come together in the same manner as bodies fall to 

 the earth. This property appears to lie within the molecular forces 

 of the body and seems to have a circumscribed and limited area of 

 action. If a center is assumed in the form of a molecule, this area 



