14 THE PRESIDENTIAL ADDRESS. 
in 1920 it had fallen to 124 per 100,000, a fall of 69°3 per cent. He also points 
out that the ‘ recent acceleration of rate of reduction which is noticeable 
in England and Scotland is of arresting interest.’ 
‘In Scotland the acceleration of fall in the mortality rate likewise 
arrests attention. Thus, during twenty years up to 1890, the percentage 
fall in mortality from all forms of tuberculosis was 35, while during twenty 
years from 1900-1919 the percentage fall was 45.’ 
This is very satisfactory, and has only been arrived at by hard work 
on the part of medical men, nurses, and voluntary workers. Any Tuber- 
culosis Scheme, however perfect in theory, will require untiring energy, 
patience, and perseverance to bear fruit. On this side of the Atlantic, in the 
United States, these anti-tuberculosis schemes have been pursued with 
enthusiasm, with the result that Washington in 1920 had a death-rate, from 
all forms of tuberculosis for 100,000 of the population, of only 85, Chicago 
97, and New York 126. London in the same year had a death-rate of 127, 
practically the same as New York. Other nations have not been so energetic 
in preventive measures, Vienna having in 1920 a death-rate of 405 and 
Paris 279 per 100,000 from the same cause. 
It is evidently the duty of every nation to take up arms against a 
disease which exacts such a terrible toll of death, suffering, and inefficiency. 
If this were done with energy and enthusiasm it is not too much to hope 
that in a few generations the tubercle bacillus would be practically brought 
under control, and with it many other malign influences. 
INFECTIOUS DISEASES.—(B) PROTOZOAL. 
I shall now pass on to the consideration of the second great group of 
infectious diseases, the Protozoal, and consider what methods of prevention 
have been found applicable to them. 
The scientific study of the protozoal diseases of man may be said to 
have begun with the epoch-making discovery of the malaria parasites in 
1880, by the illustrious Frenchman, Laveran ; next, in 1893, the discovery 
by Theobald Smith and Kilborne of the cause of Texas fever and the part 
played in its dissemination by the cattle-tick ; in 1894 the discovery of the 
trypanosome of nagana and its intermediate insect host the tsetse-fly ; in 
1898 the working out of the development of the malaria parasite of birds 
in the mosquito by Ronald Ross, greatly aided and abetted in the work by 
Patrick Manson, which led, through the work of Grassi and _ his fellow- 
workers in Italy, to the final solution of the malaria problem. A year later 
the important discovery of the mosquito carrier of yellow fever was made 
