100 



tap water. It must be assumed, therefore, that some other 

 constituent of the tap water, possibly magnesium, added its 

 effect to that of the calcium and was similarly antagonized by 

 sodium. 



A number of experiments were next performed in which 

 m/8 sodium chloride in distilled water was used as the bathing 

 fluid. In this good contractions of the rectum and rectal 

 glands were always observed, excepting in the case of nearly 

 moribund flies which were just about to discharge larvae or 

 had already done so. Peristalsis of the intestine, however, 

 was almost invariably absent. Experiments were then per- 

 formed in which varying proportions of calcium chloride were 

 added to the sodium chloride solution, namely, one, two, three, 

 or four molecules of calcium chloride per fifty molecules of 

 sodium chloride. The remarkable result was then obtained 

 that an increase in the proportion of calcium favoured 

 intestinal while actually inhibiting rectal contractions. Thus 

 while the proportion of 50 mols. NaCl to 1 mol. CaCU gener- 

 ally permits simultaneous contraction of the intestine and of 

 the various segments of the rectum, the proportion of 50 mols. 

 NaCl to 4 mols. CaCl2 either immobilises the entire prepara- 

 tion or, more usually, induces powerful peristalsis of the distal 

 intestine while absolutely inhibiting the contractions of the 

 rectum and rectal glands. The following protocol of a typical 

 experiment illustrates this fact, a 4- indicating contraction 

 and — absence of contraction. The period of exposure to each 

 solution was five minutes. The preceding solution was always 

 drained off from the preparation by means of filter paper, 

 taking care not to actually touch the preparation, before the 

 new solution was applied : — 



Table 1. 

 Experiment No. 32. 



CI 1 -L • 



Post. 



Rect. 



Ant. Rect. 



Dist. 



Solution. 



Rect. 



Gl. 



and Valve. 



Int. 



NaCl 



... + 



+ 



- 



- 



50 NaCl+1 CaCl.. 



... + 



- 



- 



+ 



NaCl 



... + 



-1- 



- 



— 



50NaCl + lCaCL. 



... - 



- 



— 



-f- 



NaCl 



... + 



4- 



- 



— 



50 NaCHl CaCl, 



... - 



- 



— 



-1- 



NaCl 



... -1- 



+ 



- 



— 



SONaCl + lCaCi 



... - 



- 



- 



+ 



The optimal ratio of ^ for the maintenance of intestinal 

 and rectal contractions, respectively, varied considerably in 

 different preparations. In the instance cited, the proportion 



