112 Transactions of the South African Philosophical Society. 



In a restricted sense the word pharmacology is often used as 

 denoting scientific investigation with regard to the remedies 

 mentioned in the pharmacopoeias, and especially in connection 

 with the needs of medical practice. The term has, however, a 

 much wider meaning, under which the scope of the investigation is 

 enlarged so as to comprise all chemical principles capable of acting 

 beneficially or otherwise upon the human system. During the 

 course of such investigations questions are frequently presented for 

 settlement which, though not falling directly within the sphere of 

 medical practice, are yet of great value in leading us to understand 

 the nature of certain materials which the physician either already 

 employs in his practice or would so employ if the potentialities of 

 such an agent were more clearly grasped. 



" Fire and water " — so runs the old proverb — " are good servants, 

 but bad masters." One scarcely needs to be a physician or a 

 chemist in order to realise that a very similar aphorism may be 

 applied to many of the remedial agents employed in medical 

 practice at the present day. An ounce may cause speedy death, 

 but a few grains may save life, or, to come within still narrower 

 limits, we know that of the powerful alkaloids a single grain would 

 bring about a fatal result, whereas the twentieth part of a grain may 

 restore circulation where the heart has all but ceased to beat. We 

 may even proceed further, and, under special conditions, avert a 

 fatal issue by using that which, in ordinary circumstances, would 

 act as a poison. To exemplify : Atropine, as we know, produces an 

 effect which shows itself in the dilation of the pupil of the eye : 

 physostigmine has the opposite effect — it causes the pupil to contract. 

 Each of these would, in this respect, act as the antidote of the 

 other, and so restore equilibrium. But equilibrium may be disturbed 

 by other means than the ingestion of a poison, and if the physician 

 is aware of some principle, ordinarily considered poisonous, but 

 whose poisonous action tends in a direction diametrically opposite to 

 that of the disturbing cause, then judicious administration of what 

 would otherwise be a poison may restore health. Take a simple 

 case in illustration : Digitalin increases the force of the heart's 

 contraction, and contracts the muscles so powerfully, when taken in 

 large doses, that the heart may remain contracted, causing death. 

 Now when, in certain forms of heart disease, that organ becomes 

 enfeebled, and fails to contract regularly with sufficient power to 

 project the blood through the arteries, the administration of small 

 doses of digitalin, by causing a more powerful contraction of the 

 muscles of the heart, may restore a failing circulation. 



It is obvious that if we know wherein the action of a poison 



