HOMO MILITAXS 



various microbes mutually attack each other in this case as well. Fol- 

 lowing the isolation of Actinomyces griseus, antagonist of Mycob. tuber- 

 culosis, it became possible to isolate also the chemical entity, now 

 designated as streptomycin, which the actinomycete uses to maintain 

 itself in the struggle for existence. Even though streptomycin has been 

 found not always to be entirely innoxuous to human beings, surpris- 

 ingly good results have already been achieved with it in cases of some 

 special types of tuberculosis. 



There is yet another matter I wish to call to your attention. It might 

 be felt that by now the microbiologist should be in possession of a 

 complete catalogue of all invisible forms of life that may directly 

 threaten man's health, thus eliminating the element of surprise in the 

 course of the subsequent fight against disease. The reply is, however, 

 that this notion is incorrect, and that during recent years diseases have 

 appeared of which it may be assumed on good grounds that they did 

 not formerly exist. 



Fortunately we can immediately counter that there are equally 

 sound reasons for believing that other infectious agents, which in pre- 

 vious centuries have caused great ravages, have meanwhile died out. 

 As an example of the latter I may mention the 'English sweating sick- 

 ness', first described in 1485, but about which nothing more has been 

 heard since 1552. 



The first epidemic broke out after the battle of Bosworth ; it led to 

 a disbanding of the victorious troops under Henry VII, whose coro- 

 nation consequently had to be postponed. The disease spread over all 

 of England; the mortality was very high; only one of every 100 per- 

 sons attacked escaped with his life. Later epidemics occurred in 1507, 

 1518, 1529, and 1 55 1 ; partly these spread even as far as the continent. 

 Thereafter no one has ever again heard of a disease with symptoms 

 such as those attending the sweating sickness. A similar situation is 

 encountered in the case of a somewhat related, but nonetheless clearly 

 distinguishable disease, known as 'la suette des Picards', because it 

 was in Picardy that it first occurred. 



After this excursion into the realm of vanished diseases I return to 

 the subject of the 'new' ones, which implies a warning that the future 

 fight against invisible life should not be underestimated. 



In this connexion some introductory remarks are in order anent 

 the origin of parasitism. It appears that there are but few disease- 



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