240 EXPKIILMENTAL INVESTIGATION OF THE ACTION OF MEDICIXES. 



disease, and the ways in which they will modify eitlier tlie 

 direct or indirect action of remedies, really are, can only be 

 determined by an increased knowledge of pathology and by 

 actral clinical observation. 



Chemical Constitution and Physiologic d Action. — T ha\e 

 spoken thus far only of the changes in the body and tlie 

 various effects which they produce ; but I must not leave this 

 subject without mentioning the wide field of research vvhicii 

 has been opened up by the remarkable discovery made by 

 Drs. Crum Brown and Eraser,* of the relation which exists 

 between chemical constitution and physiological action. It was 

 known before that one drug would act only on one part of the 

 body, another on another; but they have shown that changes 

 in the chemical composition of a drug may not only alter its 

 action, but transfer it to a different structure : so the addition 

 of sulphate of metliyl to strychnia, brucia, or thebaia, causes 

 them to act on the terminal branches of motor nerves instead 

 of on the spinal cord, while a similar addition to other alkaloids 

 removes some of their actions but leaves othei'S unchanged. 

 Further researches of this kind may enable us to determine 

 what parts will be acted on by a drug after a definite change 

 has been effected in its chemical constitution; and the progress 

 of physiological chemistry in ascertaining the composition and 

 properties of the tissues renders it not impossible tliat such 

 knowledge may yet be acquired as that spoken of by Locke in 

 the following words : " Did we know^ the (mechanical) affections 

 of the particles of rhubarb, hemlock, opium, and a man, as a 

 watchmaker does those of a watch, whereby it performs its 

 operations, and of a file, which by rubbing on them will alter 

 the figure of any of the wheels, we should be able to tell before- 

 hand that rhubarb will purge, hemlock kill, and opium make a 

 man sleep." And even though our knowledge should never 

 reach this extent, the rapid advances which it has made of late 

 years, the power which we now possess of altering the chemical 

 composition of the organic alkaloids, and along with it their 

 physiological action, and the fact that two of them (conia and 

 muscaria) have already been made synthetically, incline us to 



* Trausaeiions of the Hoyal Society of 'Edinburgh, vol. xxv, pp. 1 and 693. 



