Sensory reactions of Holothuria surinanieusis. 289 



assiiim Chromate ) ammonium chloride ) potassium sulphate ) 

 magnesium chloride (N/10). 

 Carbohydrates (Table XIX), 



maltose > (dextrose) cane sugar, (M/10). 

 Alkaloids (Table XIX), 



atropine sulphate > strychnine sulphate / quinine hydrochlo- 

 ride (M/lOO). 

 Holothuria is reactive to substances which on the human tongue 

 give rise to the four distinct taste qualities, — salt, sour, bitter, 

 sweet, — and reacts also to potassium hydroxide, representing the 

 ^'alkaline taste''. The case of the sweet substances is especially 

 interesting. Parker (1912, p. 228) believes that aquatic vertebrates 

 are insensitive to stimulation by sugars and the like, and that the 

 acquisition of such sensitivity by higher forms is possibly associated 

 with the storage of carbohydrates in terrestrial vegetation. His 

 experiments, and those of Sheldon (1909) on the dogfish which gave 

 the same result, were made only with cane sugar (and, in Sheldok's 

 experiments, dextrose). I found that Holothuria was likewise insen- 

 sitive to cane sugar even in saturated solutions. The same was 

 true of dextrose. But maltose in M/10 solution gave good reactions, 

 as did glycerin also. I therefore believe that fishes and other 

 aquatic animals may very probably be found reactive to sugars and 

 other "sweet" substances when a larger range of "sweet" stimulants 

 has been investigated. 



The lack of reaction to rain water and to saturated cane-sugar 

 solutions is sufficient evidence that the stimulus by dissolved sub- 

 stances is not osmotic. It is significant that the limiting stimula- 

 tion-concentrations of HCl (M/500 +), KOH (M/500), KCl (M/500 +), 

 acetic acid (M/500 -{-), and maltose (M/10) are of the order of magni- 

 tude w^hich we associate with taste. Evidence from the electrolytes 

 used shows that both anions and kations play a rôle in the stimulation 

 process. The reaction-time measurements with the chlorides, for example, 

 give series which vary somewhat with the part of the animal con- 

 sidered, but taking the tentacles alone the order is (Table XIII): 



K > Na > Li, NH^ > Mg 

 and the three salts of potassium used give, for the same part, 



the series: 



CI > SO,, CrO, (M/10) 



The tables of reaction times also show peculiarities which have 

 been recognized in the chemical stimulation of other animals. Com- 



