346 W. J, CKOZIER 



tracted. This was unlike the condition in solutions of NH4CI 

 and KCl, where both cloaca and anal sphincter were tightly con- 

 tracted. The absence of any pulsation in 5/8 M NH4CI and in 

 5/8 M KCl is partly a secondary result, since solutions of these 

 salts are powerful sensory stimulants for the skin of holothurians 

 (Crozier, '15), which produced contractions from which the 

 cloacal ends did not recover before the toxic action of the solu- 

 tions led to death. 



That the single electrolytes LiCl, NH4CI, and KCl are toxic, 

 is also indicated by the results of tests in which several concen- 

 trations of these substances were compared (table 10). These 

 experiments showed that with LiCl the duration of rhythmic 

 movement and of irritability was greater at 5/16 m than at 5/8 m 

 concentration, and that with NH4CI and KCl the duration of irri- 

 tability was also greater at the lower concentration, even though 

 in the case of the more dilute solutions an osmotic factor (see 

 previous section) was also working to produce death. 



NaCl is thus the only single constituent of sea water which will 

 maintain pulsation and irritability for any considerable length 

 of time, and in this respect it is only partially imitated by LiCl 

 — a fact further proven by the physiological incompleteness of 

 a van't Hoff solution made up with LiCl in place of NaCl, in 

 which the pulsation of a cloacal end endured for about 45 

 minutes. 



The comparative effects of MgCU and MgS04 were of particu- 

 lar interest. Spaeth ('13, p. 553) found that MgS04 exerted a 

 more powerful action upon the melanophores of Fundulus than 

 did an iso-ionic MgCl2 solution. Table 11 contains the data from 

 experiments in which MgCU and MgS04 were compared at several 

 concentrations by means of their action on cloacal pulsation in 

 Stichopus. The result of these tests was that MgS04 appeared 

 to have a distinctly higher anaesthetic power than MgCl2. 



h) Mixed salts. As the basis for the experiments made with 

 mixed salts there was employed a van't Hoff solution of the 

 composition: 5/8 m [100 NaCl + 7.8 M^Cla + 3.8 MgS04 + 2.2 

 KCl + 2.5 CaCy (cf. Mayer, '11, 'U^). The solutions were 

 made up in rain water. The averages obtained for the time of 



