LEI HAL DOSE — ADMINISTRATION — EXCKETION. 251 



tion, to secreting nerves; and full or empty bladder, and 

 diminished or increased peristalsis, to the motor nerves of the 

 bladder or intestine. We then try the effect of a small dose 

 and note in what respect it differs from that of a large one. 

 We thus ascertain in a general way what the organ is, which 

 is chiefly acted on by any drug, and afterwards proceed to 

 investigate the nature of the action by a farther scries of 

 experiments. 



Minimum Fatal Dose. — If the drug be poisonous, we then try 

 to ascertain tlic minimum fatal dose. For this purpose we. 

 weigh an animal and inject into it a dose which we think will 

 not prove fatal, wait a short while, and then inject more till 

 death is produced. We then reckon how much of the drug has 

 been injected for every pound weight of the animal. We take 

 another animal, and inject into it at once a quantity which will 

 be somewhat smaller for its body-weight than that given to the 

 first. The reason why a somewhat smaller quantity should be 

 taken is, that some time was allowed in the former experiment 

 for the excretion of part of the poison betw^een each dose. If 

 this amount prove fatal, we must give a still smaller quantity 

 to another animal ; but, if not, we must give more till we find 

 the smallest quantity which will kill. 



Various Channels of Administration, — The next point to be 

 determined is, whether the effects are the same when given by 

 the mouth or rectum, or other mucous surfaces, as by sub- 

 cutaneous injection. If we should find, as Bernard did with 

 curare, that a substance which is active when injected sub- 

 cutaneously or into a vein, has no effect when introduced into 

 the mouth, rectum, eye, or bladder, we must determine whether 

 this is due to want of absorption or to decomposition of the 

 drug by the secretions with which it becomes mixed. This is 

 clone by mixing it with these secretions, such as urine or gastric 

 juice, allowing it to stand some time at the temperature of the 

 body, and then injecting the mixture subcutaneously, and 

 observing wliether tlie usual effect is produced or not; or by 

 ligaturing the ureters to prevent excretion. 



Excretion. — Lastly, we examine in what manner it is excreted 

 from the body. As most solids are excreted by the kidney, we 



