COMMON CHEMICAL SENSE 6 



1. High concentrations of acids (i^), salts (2n), alkalies {^) 

 and alkaloids (loo). which evoke prompt and vigorous reactions 

 from the earthworm, Eisenia foetida, cease to cause any dis- 

 turbance the moment the stimulant is washed off by immersing 

 the animal in water. If any serious disintegration were produced 

 by these solutions, it would be reasonable to expect the continu- 

 ance of activity after the external supply of the stimulant had been 

 removed. - 



2. Holothurians, such as H. surinamensis (Crozier, "15 c) 

 and Stichopus moebii (Crozier, '15 b), possess skin pigments 

 whose loss is a fairly good indicator of changes in permeability. 

 Yet in no case on the application, by the pipette method, of the 

 stimuU used by Parker ('12) was there any indication of pigment 

 loss accompanying reaction.-^ This is true also of the nudi- 

 branch, C'hromodoris zebra. 



III. The value of the intracellular indicator of ("hromodoris 

 in the study of cell penetration by acids has been pointed out 

 elsewhere (Crozier, 'lob). When small volumes of acids, 

 even in rs solution, are used to stimulate ( "hromodoris, there is 

 no visible evidence that they penetrate the skin. In fact the 

 time required for the penetration of the acids is quite high 

 (see also Harvey, '14), the most rapid rate observed being with 

 ^0 iso-valeric acid, where penetration recjuires 1.5 minutes. 



- Experiments with earthworms also disclose certain important deficieni-ie.s 

 in'^thc method wherol)y the animals to be tested arc entirely immersed in the 

 stimulating solution. If the reactions are to be studied quantitatively, there 

 are features undoubtedly obscured by this procedure. For example, the time 

 elapsing between the complete immersion of an earthworm (P^iscnia foetida i 

 in a tV lithium chloride solution and the instant the first writhing movement 

 apjjcared, was found to be at least ten times greater than the reaction time of the 

 same worm when part of it (the anterior end) was stimulated. The speed of 

 reaction is in part conditioned by the number of receptors afTected, i)ut this 

 does not analyze the situation completely. It is quite probable that the re- 

 sponses ol)served by Coghill are not at all due directly to .sensory stimulation by 

 acid. 



•^ I have observed that under certain circumstances Ptychodera sp. — a Ber- 

 mudan enteropneust — reacts to chemical irritation by extruding a yellowish 

 pigment. There is ground, ho\vever, for believing that this is an instance com- 

 parable to that of Lumbriconereis (Kschischkowski, '12), in which K salts have 

 apparently a more or less specific action in producing the response. 



