PHYSIOLOGY OF SYNAPTULA HYDRIFORMIS 371 



reactions of Synaptula to sugar and glycerine simply with an 

 osmotic pressure phenomenon, and not with a response com- 

 parable to our gustatory sensation of sweetness. The close 

 correspondence of the limiting concentrations for stimulation 

 by increased osmotic pressure (1) when the sea- water is concen- 

 trated by driving off water and (2) when sugar or glycerine are 

 added, shows that the method is at least consistent with itself. 



Saccharine, however, proves to be very stimulating. Whether 

 Synaptula actually experiences a sweet sensation from a solu- 

 tion of saccharine, it is impossible to state. In man saccharine 

 is sweet to the tip of the tongue, but rather bitter to the back 

 of the tongue. This difference is more pronounced in parabrom- 

 benzoic sulphinid, a bromine substitution product of saccharine 

 (Howell, '16, p. 298). It may be possible that in Synaptula 

 only a bitter (alkaloid) effect is perceived when the animal is 

 stimulated by a solution of saccharine. 



Of the three acids tried, HC1 caused a response at the lowest, 

 acetic at a slightly greater, and oxalic at a still greater concen- 

 tration. Neglecting the suppression of ionization of HC1 due 

 to the presence of Cl ions already in the sea-water, the effect 

 of which is very slight (Chick, '13, p. 333), there would be in 

 1/600 M HC1 a hydrogen ion concentration of about 0.0016 TV, 

 since HC1 at that dilution is practically wholly dissociated. 

 But acetic acid at 1/400 M is slightly less than 8 per cent dis- 

 sociated, therefore the concentration of the hydrogen ion in the 

 limiting concentration of HC1 for stimulation is some 8 times 

 that in the limiting concentration of acetic acid. This is exactly 

 the phenomenon to which Crozier ('16 a) refers as occurring in 

 human taste. He suggests, as an explanation of this anomaly, 

 that " potentially ionizable hydrogen" is present " within the 

 undissociated acid molecules, though secondary ionization may 

 also play a part." 



Two alkaloids only were tried, strychnine and quinine. The 

 former is the more stimulating (cf. Crozier, '14 a). The sensi- 

 tivity of Synaptula to these reagents is remarkable. It re- 

 sponds to a solution of 1/10,000 If quinine; but even in man 

 the limit is only 1/26,000 M (Parker, '12). After stimulation 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 24, NO. 2 



