INTRODUCTORY AND GENERAL 7 



strength. These agents are all-important in medical treatment 9 

 but in themselves they are useless, and they only act by hastening 

 the evolution of the immunity, without which the disease must 

 necessarily progress to a fatal issue. This is well seen in the few 

 diseases in which the development of immunity, in face of a natural 

 infection, is but slight, or perhaps altogether absent, such as 

 leprosy or hydrophobia. Here ordinary medical treatment is 

 powerless, and all our hopes for the future are concerned with the 

 discovery of a direct specific remedy. 



It is this connection between immunity and recovery that 

 renders the subject so important to the physician, and the neglect 

 with which its study is treated by the general members of the pro- 

 fession a matter of such profound regret. In our medical educa- 

 tion at the present day we pay, and rightly, much attention to the 

 study of physiology, for without a knowledge of the processes of 

 the healthy body we can hardly hope to diagnose and treat its 

 derangements when diseased; and our physicians are in many 

 cases competent physiologists. But it is equally important to 

 understand the method in which the diseased body combats and 

 cures an infection ; and, although our knowledge of this is as yet 

 imperfect, it is increasing day by day, and results of the greatest 

 interest to the practising physician have already been obtained. 

 And I, for one, think that an intelligent appreciation of what is 

 actually taking place in the body, of the conservative and adverse 

 forces, and of the conditions necessary for cure, will always be of 

 value to the therapist, although it may not give any definite 

 information as to what drug is to be prescribed. 



Let us revert to the subject of NATURAL IMMUNITY. We may 

 define it roughly as the immunity possessed by a certain individual 

 in virtue of its belonging to a given animal species ; it is inherent 

 to a greater or less extent in all members of that species, and is not 

 dependent on any event taking place during the life of the animal 

 in question. In most cases it is present at birth, though this is 

 not absolutely essential. 



Examples are numerous. The lower animals are immune to 

 the gonococcus, and, with few exceptions (the higher apes), to 

 syphilis also. On the other hand, most of the diseases of the 

 lower animals do not affect man fowl cholera, canine distemper, 

 and rinderpest are a few of many examples. In some cases all 

 animals, with a few exceptions, are immune : this is the case with 

 the venereal diseases, and in some of the protozoal infections of 



