ACTION IN HEALTH AND DISKASE. 230 



are removed, we are, I think, justified in concluding that, when 

 the organs or structures on wliich a drug acts are similar in 

 man and the lower animals, the action will be alike, and that 

 variations will be observed just in proportion to the difference 

 between his structure and theirs. But as it ma}' be difficult or 

 impossible to detect these differences except from the effects, 

 we ought to test our conclusions as to the action of remedies 

 by giving them to a healthy man, and observing whether their 

 effects are such as we have been led, from our experiments on 

 animals, to expect. 



Disease. — The different effects of a medicine in health or 

 disease may be partly due (1st) to alterations in the relative 

 amount of absorption or excretion produced by the disease and 

 consequent changes in the quantity of the drug actually present 

 in the blood. Thus, enormous quantities of opium have been 

 given during the collapse of cholera without producing any 

 effect, because no absorption took place, and the opium re- 

 mained in the stomach so long as the collapse persisted. When 

 it passed off aud absorption again began, the opium was taken 

 into the circulation and exerted its usual action, so that persons 

 have died of the remedy after recovering from the disease. 



The difference in action is due (2nd) to the alterations pro- 

 duced by disease in the organs and tissues of the body which 

 may interfere with both the indirect and direct actions of the 

 drug. Thus, digitalis usually slows the pulse by acting on the 

 heart through the vagus. But in febrile diseases it sometimes 

 has little or no perceptible action on the pulse. This is prob- 

 ably due to the fact, that the accelerating ganglia of the heart 

 are stimulated by the high temperature to such an extent that 

 the vao-us can no loncrer restrain them. For irritation of the 

 vagus trunk by galvanism, which has a stronger action on the 

 heart than digitalis and usually stops its pulsations entirely, 

 ceases to do so when the temperature of the animal is raised, 

 and yet the vagi are not paralysed, for when the motor power 

 of the heart diminishes they can again stop it, although the 

 temperature may still be high.* What the alterations in each 



* Lauder Brunton, " On the Action of Heat upon the Mammalian Heart*" 

 8t. Bartholomew Sospital Beports, vol. rii, p. 221 (vide p. 212). 



