512 S. O. MAST 



EFFECT OF ALKALIS 



Experiments on the effect of changing the alkahnity were made 

 at eight different times by adding sodium hydrate directly to the 

 culture fluid containing positive colonies. Reversion was not 

 obtained in any of these experiments, with the possible exception 

 of those in which the colonies had been made positive by the addi- 

 tion of acid, and in none of these were the results clear-cut and 

 definite. 



Dilution of the culture fluid with pure distilled water also failed 

 to produce definite results. The effect of such dilution in various 

 degrees was tested in experiments made at nine different times. 

 In four of these series of experiments the addition of pure water 

 had no observable effect on the sense of orientation. In five the 

 colonies became slightly positive when the pure water was added. 

 To begin with, the colonies used in these five experiments were 

 not strongly negative, and they soon became negative again 

 after the water had made them slightly positive, and now the 

 addition of more pure water did not make them positive again ; 

 on the contrary, it appeared to make them more strongly negative. 

 It is consequently evident that reduction of alkalinity due to the 

 addition of pure water was far less marked in its effect on rever- 

 sion in orientation than reduction produced b}'' the addition of 

 acids. The results obtained bj^ mixing culture solutions differing 

 in alkalinity, as described below, were, however, quite as marked 

 as those obtained by adding acids. 



A total of nine series of tests were made in studying the effect 

 of such mixtures on the sense of orientation. In some the alka- 

 linity was increased, in others it was decreased. The concentra- 

 tion of the alkaline in the solution used was changed either by 

 slow evaporation or by adding sodium hydrate. The results 

 obtained were definite in every test. They may be summarized 

 as follows: 



1. Negative colonies in a culture solution concentrated by 

 evaporation become definitely positive if fresh culture solution is 

 added. 



2. Positive colonies in fresh culture solution become definitely 

 negative if culture solution concentrated by evaporation is added. 



