388 Leo 



A solution ol" follitline, 1 in J 000 in saline, was applied to such a piepaia- 

 tion; the movements were promptl}'^ inhibited and the tonus diminished. 

 Nicotine, 1 in 1000, was then applied; the muscle entered into tonic 

 contraction, the waves for the time ceasinor, but it soon regained its normal 

 activity. Pyridine, 1 in 1000, was administered and produced hardly any 

 result; collidine was applied once more, when it again produced its typical 

 effect. 



It is clear from this that nicotine and collidine aci in opposite directions : 

 the former causes the muscle to increase in tonus, the latter inhibits move- 

 ments and causes it to relax : pyridine, in these doses, is almost without 

 action. 



ii. The Heart. — It has been pointed out that experiments made by 

 dropping drugs on the frog's heart are not likely to lead to valuable results, 

 since in many cases the action differs from that obtained when the drug 



Time. 



Fig. J. — Record of movements of an isolated frog's heart perfused through the hepatic vein. 

 A sliow,-; the elTect of 01 per cent, nitotiiu'. B shows tlie effect of 01 i>er cent, colliiline. Time. 30 secnmls. 



passes through the circulation of the heart. The following experiments on 

 the isolated frog's heart were therefore performed by perfusing Ringei's 

 solution through one hepatic vein and allowing it to escape by the aorta, 

 the heart-beat being recorded by the suspension method. A solution 

 of I in 10,000 nicotine raised the tonus of the heart muscle and slightly 

 quickened the beat. The same strength of pyridine produced no eifect, 

 while tlu^ same strength of collidine produced some slowing and a fall 

 in tonus. A more concentrated solution of nicotine (1 in 1000) always 

 causes the heart to enter into very marked tonus. The effect of pyridine 

 (I in 1000) slightly weakens the beat of the heart; it never produces 

 a rise of tonus. 



From such experiments it is sixown that nicotine has much the most 

 toxic effect on the heart, and that pyridine has the least. The effect of 

 collidine compared with nicotine is shown in fig. 1. It will be noticed in 

 these experiments, which were performed under identical conditions, that 

 the nicotine (A) quickens the heart at first, but later causes some slowing • 



