c8 H. G. Krtbs 



placed in the several threshold solutions. It is obvious that 

 immersion in these solutions presents to the animal membranes a 

 more concentrated fori'i of the chemical than they experienced 

 under a localized impingement introduced through the pipette. 

 After noting carefully the flow of the current from the pipette to the 

 animal, which can readily be seeP' under the microscope, however, 

 I am inclined to believe that differences m concentration due to 

 diffusion are not significant. The vatio between the various 

 stimuli will hold in either case. 



When placed in N/3000 mineral acid solution the animals soon 

 developed increased peristalsis and exhibited various twisting and 

 stretching movements. They seemed to be normal on the following 

 day. In N/2000 these movements were accentuated. The 

 animals died within a day or two. A similar experience followed 

 the use of N/2000 and n/iooo of the organic acids. N/i500 of the 

 tiydrates was fatal in four or five days. The ^olosoma, however, 

 seem to be able to live indefinitely in N/1200 carbonate solution. 

 The threshold solutions of the halides were fatal in a day o** two, 

 n/io,ooo FeSO^ was not fatal in four or five days, N/5000 was 

 fatal in a few hours. The threshold stimulations of zinc ?nd 

 copper sulphates are not injurious to the animal. N/40000 of the 

 zinc solutions, however, is fatal within 24 hours, that of the copper 

 not within two days. 



The evidence furnished bv these facts in not very consistent. 

 From the pomt of view of a positive or a negative reaction to a 

 localized stimulus, however, we conclude that the reactions of 

 yTyolosoma to the threshold solutions of these chemicals may be 

 correlated w^ith their relative toxicity. 



Nervous System and the Stimuli 



Does the presence of a nervous system play a significant part in 

 threshold reactions? To this test two series of experiments were 

 used. In the first case the head segment was severed from the 

 rest of the body with a pair of sharp needles. The cut surface 

 healed over in a very short time. After several hours the above 

 threshold experiments were introduced with negative results. 



