508 S. O. MAST 



Formalin, sugar, oxygen, hydrogen peroxid, all of the alkalis 

 tested (NaOH, KOH, NH4OH) and all of the salts tested except 

 ammonium chlorid (MgS04, NaCl, CaClo, KNO3) have no appre- 

 ciable effect on the sense of orientation. 



These results, as presented, throw but little light on the ques- 

 tion as to the factors involved in reversion. Let us, therefore, 

 consider in detail the effects of the substances mentioned. 



EFFECT OF ACIDS 



If a little acid is added to a solution containing negative 

 colonies of Spondylomorum, they usually become strongly 

 positive almost immediately, but they soon become negative 

 again. If nov/ more acid is added, they become positive again, 

 but in a few moments they are again negative. Thus they con- 

 tinue to become positive after every addition of acid and then 

 negative again until they are killed. These features in the 

 response of Spondylomorum are clearly brought out in the fol- 

 lovring details regarding two experiments: 



1. On November 27, at 2.40 p.m., numerous colonies were put 

 into a watch-glass containing about 1 cc. of solution from the 

 culture jar and exposed in diffuse daylight. The colonies imme- 

 diately collected at the side of the watch-glass away from the 

 source of light. They were strongly negative. At 2.51 p.m., a 

 trace of 10 per cent sulfuric acid was added, the solution being 

 thoroughly stirred at the same time. At 2.53 p.m., the colonies 

 were clearly shghtly positive; but at 2.55 p.m., they were begin- 

 ning to become negative, and at 3.00 p.m., they were strongly 

 negative again. A trace of acid was now added, after which the 

 colonies immediately became fairly strongly positive; but at 3.03 

 p.m., they were again negative. More acid was added at this 

 time, and the colonies again immediately became distinctly 

 positive. At 3.06 p.m., they were again negative. Acid was 

 again added, and reversion followed immediately with a return 

 to negative orientation at 3.10 p.m., when the process was again 

 repeated with the same results. A trace more acid Avas now 

 added. The colonies became inactive, but in a few moments 

 thej^ became active again and swam definitely toward the light, 



