232 EXrERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



each tissue will only receive half as much of it. The dose of a 

 drug must therefore be regulated by the weight of the patient ; 

 and thus womgn, being lighter, require a smaller amount than 

 men, and children less than adults. Though it would be more 

 exact, it is not always convenient, to weigh patients ; but in 

 experiments on animals the weight of the animal should always 

 be carefully ascertained, as well as the amount of the drug 

 administered. If a substance be injected into the veins, the 

 whole of it mixes with the blood and becomes active imme- 

 diately, and the maximum effect is thus at once obtained and 

 will again diminish as the substance is excreted. But the case 

 is dilferent if it be injected subcutaneously, and if it be given 

 by the stomach or any otlier mucous cavity the difference is still 

 greater ; for as soon as some of it is absorbed excretion begins, 

 and thus part of the drug is passing out of the blood while 

 another part is being taken in. The amount in the blood is, 

 then, only the difference heticecn that ahsorhed and that excreted in a 

 glveyi time, and absorption may be so slow or excretion so quick 

 that there is never a sufficient amount of the substance in the 

 blood to produce any effect. Thus Bernard found that a dose of 

 curare which would certainly paralyse an animal wdien injected 

 into the veins or even subcutaneousl}^, would have no effect 

 when introduced into the stomach;* and showed that this 

 was due to the kidneys excreting the poison as fast as it was 

 absorbed irom the stomach, by extirpating the kidneys,! when 

 the animal became paralysed as surely as if tlie poison had 

 been introduced at once into the veins, thougli not so quickly. 

 Hermann also discovered, without being acquainted with 

 Bernard's observations, that curare taken into the stomach 

 would produce paralysis if excretion were prevented by ligature 

 of the renal vessels. 



The more rapid the absorption, or the slower the excretion, of 

 any drug, the greater will be its effect. Thus the effect produced 

 by the same dose of a medicine will be in proportion to the 

 rapidity of its absorption from the different parts to which it 

 has been applied, unless the differences be so slight or the excre- 



* Bernard, Leqons sur les Eff'eis dest Suhstan"PS! Toxiques, p. 282. 

 t EernarJ, Eecue des Cuurs Scientijiques, 1805. 



