230 EXPERIMENTAL INVESTIGATIOX OF THE ACTION OF MEDICINES, 



up more of one thing and some more of another. And they do 

 just the same with drugs added to the nutritive fluid. Thus 

 lime salts naturally exist in the blood, and are carried by it to 

 every part of the body; but while the bone-eells take them up 

 in large amount, nerve-cells assimilate an almost infinitesimal 

 quantity.* And if we feed an animal on madder, which has an 

 affinity for lime-salts, the bones become deeply stained, while 

 the nerves and fat retain their normal colour. It is possible, 

 too, though experiments on this point are wanting, that a sub- 

 stance added to the nutritive fluid ma}^ be taken up by two 

 structures, but may have a very different effect on the one from 

 what it has on the other; just as a grahi of sand, which would 

 have no effect on the machinery ol a locomotive, may totally 

 stop the movements of a watch. We do not know whether 

 sulphocyanide of potassium and curare are taken up equally by 

 nerves and muscles or not ; but the former salt will paralyse the 

 muscles without affecting the nerves, while curare will paralyse 

 the nerves, but leaves the muscles intact.f 



The cells composing one structure, then, take up and are 

 acted on by some drugs, and not at all by others; while other 

 structures are much affected by the very substances which had 

 so little action on the first. 



Direct and Indirect Action. — When any drug is taken up by 

 a structure and acts upon it as curare on the ends of motor 

 nerves, we term this its dii^ect action. Thus paralysis is due to 

 the direct action of curare on the motor nerves. But, as all 

 parts of the body are dependent on one another, some other 

 structure may be affected, not by the action of the drug upon it 

 but by that which it has exerted on the first part. This is its 

 indirect action. Thus, when curare has been given to an animal, 

 it occasionally happens that the nerves going to the respiratory 

 muscles become paralysed before those which go to the extremi- 

 ties.J The muscles of respiration then cease to act, the blood is 

 no longer arterialiaed, carbonic acid accumulates, and, by irri- 



* Buchlieim, Arzneimittellehre, p. 25, 



t Bernard, Lec^ons sur les l^jfets des Substances Toxiques, p. 314. 

 X Hermann, " Ueber eine Bedingung des Zvistaudelvommens von Yergif- 

 tungen," Du-BoU Raymond und ReicharVs Archiv, 1867, p. 64. 



