REVERSION IN ORIENTATION TO LIGHT 507 



onies had collected either at the window side or at the room side 

 of the dish, depending upon whether they were positive or nega- 

 tive; then traces of the chemical to be tested were successively 

 added, the solution being thoroughly stirred after each addition, 

 until the sense of orientation changed or until there was no longer 

 any orientation. The solutions were then tested for alkali with 

 neutral red, and for acid with salts of neutral red prepared by 

 treating neutral red with ammonium hydrate and washing 

 the crystals produced in pure distilled water. 2) Ten watch- 

 glasses containing a given amount of solution from the culture 

 jar without any colonies were placed in the same illumination in 

 front of a window. Chemicals to be tested were then added to 

 the w^atch-glasses in such amounts as to make a series of solutions 

 differing in concentration. A drop of solution from the culture 

 jar containing colonies was then added to the solution in each 

 watch-gl9,ss and the effect on the behavior of the colonies noted. 

 In all cases the solutions were tested with neutral red. In some 

 experiments distilled water was used in place of the solution from 

 the culture jar and the colonies were w^ashed in distilled water 

 before they were used. 



In each experiment the temperature and illumination were prac- 

 tically constant throughout. 



EFFECT OF CHEMICALS, GENERAL STATEMENT 



The results obtained in reference to the general effect of differ- 

 ent chemicals when added to culture solutions may be summarized 

 as follows: 



All the acids tested (carbonic, hydrochloric, nitric, sulphuric, 

 formic, boric, chromic, tannic, tartaric, and oxalic), chloroform, 

 ether, and chloral hydrate cause negative specimens to become 

 strongly positive. They have no effect on positive specimens 

 except perhaps to make them more strongly positive. There is 

 also some evidence indicating that ethyl alcohol, ammonium 

 chlorid and pure water induce reversion from negative to positive 

 orientation, but if these substances actually have any effect it 

 certainly is far less pronounced than that produced by any of the 

 substances mentioned in the preceding paragraph. 



