390 SCIENCE PROGRESS 



the object of these notes to trace the main lines of development 

 as they reveal themselves. Owing to the exigencies of space, 

 this can only be done in outline. 



The Third Partner in Disease. — ^The last few months have 

 witnessed a definite movement away from the purely bacterio- 

 logical attitude to disease. This does not, of course, mean that 

 anyone doubts that bacteria are the causes of the diseases attri- 

 buted to them. It means rather that, taken alone, they are 

 probably not so harmful as was supposed a few years ago. 



Thus it is now generally accepted that tubercle bacilli are 

 found everywhere, and that most people harbour them at one 

 time or other. Many people seem to harbour them continually. 

 In these, however, they are purely saprophytic and inflict no 

 injury. It is only when some third factor or partner comes into 

 play that the harmless bacillus becomes the deadly parasite. 



What this third partner may be is not yet at all clear. In 

 the case of phthisis, silica dust certainly plays such a part, and 

 so gives rise to stonemason's consumption. But it is evident 

 that silica is but one of many agents which are capable of acting 

 in this way. 



Again, it has been shown recently that tetanus bacilli or the 

 bacilli of gas gangrene, if washed and then infected, remain 

 harmless. No evil effects occur unless at the same time or at 

 a later period an ionisible salt of calcium is injected. If this 

 is done, however, tetanus or gas gangrene rapidly supervenes. 

 Thus the calcium salt plays the part of " third partner," a part 

 clearly taken in nature by the dirt which usually contaminates 

 the wounds from which tetanus and gas gangrene arise. 



We may add to these two illustrations a reference to the 

 work of Besredka, of the Pasteur Institute in Paris, on immunity 

 in dysentery and the typhoid group. He found, as others had 

 found before him, that rabbits are singularly insusceptible to 

 paratyphoid infection. On the other hand, if a rabbit had been 

 given some ox-bile previously, it became highlysusceptible to this 

 disease. Thus the ox-bile (or similar intestinal irritant) seemed 

 to play the part of third partner, without which infection, even 

 in the presence of the specific germ, could not take place. 



The importance of this new trend of opinion is obvious. 

 For, in general, the efforts which have been made to prevent 

 disease by abolishing bacteria have failed completely. A new 

 hope is presented by the idea that, though bacteria cannot be 

 got rid of, the chain of events and circumstances on which their 

 activities depend can be broken. In short, if we can vary or 

 remove the third partner, we may be able to prevent the onset 

 of the disease. 



This conception bears a resemblance to the methods 

 employed in the case of tropical disease. Thus, in malaria 



