CHEMOTROPISM 143 



lower limit was a little above a 0.0U1 per cent, solution. 

 The effect of the free citric acid was a mixed one since 

 the spermatozoa were negative to H ions and positive 

 to the citrate anion. Instead of being able to use a U.l 

 per cent, solution, as in the case of the sodium salt, a 

 0.01 per cent, solution was the highest concentration to 

 which they were positively chemotropic. This means that 

 the hydrogen ion of citric acid solutions above m/1000 

 repel the spermatozoa, while wiien solutions of m/2000 

 or below are used the hydrogen ion effect no longer in- 

 hibits the positive effect of the citrate anion. In addition 

 the validity of Weber's law could be demonstrated. The 

 spermatozoa were indifferent to malates, oxalates, and 

 many other salts, as well as to sugar and proteins. 



2. "While all the botanical observers, from Buller on, 

 had found that the hydrogen ion has only a preventive 

 effect upon the positive chemotropism of lower organisms, 

 Jennings tried to show that acids have a positive effect, 

 especially when in low concentrations. 250 But his con- 

 centrations are not quite as low as he seems to assume, 

 since a 1/50 per cent, (m/180) HC1 solution, toward which 

 he believes to have proven positive chemotropism of Para- 

 mcecia, is a deadly concentration.* Jennings 's interest in 

 the problem was aroused by a phenomenon of aggregation, 

 not infrequently found in the suspensions of infusorians. 



It is well known that when certain infusoria are left undisturbed 

 they do not remain scattered, but gather in more or less dense groups. 

 Thus, if they are mounted on a slide in a thin layer of water, soon dense 

 aggregations will be formed in certain areas, while the remainder of the 



a The cells of the stomach resist a much higher concentration of HC1 

 hut this is an exception. Infusorians, fish, and organisms in general are 

 killed in a short time in m/180 HC1 or in a mucli lower concentration of 

 acid. Thus Fundulus does not live more than one hour in m/3000 HC1 or 

 HN0 3 . (Loeb, J., and Wasteneys, H., Biochem Z., 1911, xxxiii, 489; 1912, 

 xxxix, 1G7.) 



