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, rmderpest, 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 moculated 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, 
