656 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1911. 



led to the important observation that in animals previously treated 

 with dead bacilli the later inoculation of living organisms occasioned 

 an energetic local reaction, leading in some cases to their destruction. 



From his experiments he was led to the conclusion that, not only 

 could a guinea pig be immunized against tubercle by repeated injec- 

 tions of the products of tubercle bacillus, but that the same tissue 

 reaction could be stimulated, and the disease brought to a standstill 

 by this means. Later (1890) he published his well-known results 

 upon tuberculin, by means of which tuberculosis could be not only 

 diagnosed, but .in the early stages might, he hoped, be cured. The 

 possible remedy was enthusiastically welcomed by the whole world. 

 Medical men thronged to Berlin from all parts to see the results of its 

 application. The treatment was applied to all sorts of cases in what 

 we now know were colossal doses. The results were disappointing, 

 and in many cases disastrous. The premature publication of his 

 results with tuberculin was a misfortune, and the failure of the 

 treatment obscured for the time being the great value of Koch's 

 work, and even exposed him to opprobrium. Koch had, however, 

 made a great discovery, but underestimated the potency of the agent 

 he had brought to light. Tuberculin is an invaluable diagnostic for 

 early tuberculosis in man and animals, and is universally employed. 

 Since 1890 it has been consistently employed by a number of physi- 

 cians all over the world for the treatment of tubercle with what appear 

 to be beneficial results, and of recent years its employment has again 

 been resuscitated by Wright. It is now administered in much smaller 

 doses, and with careful observance of the effect of each injection. 



During the next eight years, 1891-1899, Koch was occupied with 

 investigations into a large number of diseases of men and animals. 

 The list includes leprosy, rinderpest, plague, surra, Texas fever, and 

 malaria. These investigations necessitated his spending much of his 

 time abroad. It would be difficult to judge just how much of the 

 knowledge gained upon these diseases to attribute to Koch, as he was 

 accompanied by one or more distinguished workers, as in the case of 

 the German plague commission which visited India. It is very clear, 

 however, from the published reports and papers, that the insight and 

 experience with which he directed the inquiries materially enhanced 

 our knowledge of the causation and means of spread of these diseases. 



Koch's work upon malaria needs special mention. Whilst in trop- 

 ical countries, his attention was naturally drawn to this disease. 

 Laveran's discovery of the malarial parasite had been made, but the 

 mechanism of the spread of the disease was unknown. Manson's 

 discovery that filaria "was inoculated by the mosquito, Theobald 

 Smith's proof that Texas fever was transmitted by ticks, and Bruce's 

 demonstration that the tsetse-fly disease was due to a protozoan para- 

 site, and merely conveyed by the fly, suggested to Koch, as to others, 



