CLASSIFICATIONS OF MEDICINES 21 



this horse serum itself, but there has been a change in the 

 infected animal ; it has become hypersensitive to some 

 substance or substances (probably enzymes) contained in 

 that serum. 



Attention was first drawn to this by Behring, who found 

 that during the process of the production of antitoxin cer- 

 tain animals, instead of becoming more resistant to its 

 action, became much less resistant. This anaphylaxis or 

 hypersusceptibility should be borne in mind in connection 

 with the treatment of diphtheria or tetanus, and as large 

 a dose as possible of the antitoxin should be given at once, 

 so that a second dose may not be necessary, as it is quite 

 possible that this phase of anaphylaxis may come to play 

 an important part in the condition of the patient where 

 antitoxic serum is given by repeated injections. 



CLASSIFICATIONS OF MEDICINES 



Medicines are drawn from the three great natural king- 

 doms, and are characterised by various physical and chemi- 

 cal properties : but these characters do not afford suffi- 

 ciently accurate or definite indications of the actions of 

 drugs on living bodies, and hence are not of much service 

 in practical classifications. The atomic weights of inorganic 

 elements are of little or no value in determining on what 

 organs or in what way inorganic elements and their com- 

 pounds act as medicines. The soluble salts of the heavy 

 metals are certainly generally active poisons, though neither 

 similar chemical composition nor similar chemical reaction 

 necessarily confers similar physiological effects. Sub- 

 stances which crystallise in the same form have, however, 

 somewhat similar actions, and on this isomorphous basis the 

 elements have been arranged into nine groups, in each of 

 which it is noted that the intensity of action increases with 

 the atomic weight (Sir Lauder Brunton). The same base, 

 united with different acids, produces salts which exhibit 

 very different actions, as illustrated in the several com- 

 pounds of sodium and potassium. Equally diverse physio- 

 logical effects are produced by compounds resulting from 

 conjoining the same acid with different bases. Such irritant 



