4 THE PRESIDENTIAL ADDRESS. 
to come directly or indirectly into contact with the wound, the hands of 
the operator, and the skin of the patient, to treatment with chemical 
disinfectants. 
The satisfactory results which followed this practice astonished even 
Lister, and he spent the rest of his active life in improving and simplifying 
technical methods of preventing the ingress of microbes to wounds, and in 
convincing his professional brethren of the truth of the conclusions based 
on this work of Pasteur. 
INFECTIOUS DISEASES.—(A) BACTERIAL. 
As soon as it was recognised that infectious diseases are caused by 
living germs a wave of enthusiasm swept through the medical world, 
and it was not long before the causation of many of the most important 
of them was discovered. I need not give a full list of these, but at or round 
about the time of the first meeting of the British Association in Canada 
the micro-organisms of tuberculosis, typhoid fever, Malta fever, cholera, 
malaria, diphtheria, tetanus, and others had been discovered and described. 
But it must not be assumed from what has been said that all the most 
important diseases are caused by living germs. Many of the ills that 
afflict mankind are due to quite other causes—alcoholism, for example, 
or the deficiency diseases, due to the absence or deficiency in our diet of 
some substance essential to proper growth and development. Rickets, 
one of the greatest scourges of industrial communities, is mainly a deficiency 
disease. It is reported that as many as 50 per cent. of the children in the 
slums of some of our big cities suffer from the effects of this disease. 
Then again, there is the whole series of diseases or conditions due to 
defective or excessive action of our own internal glands. 
Added to these, and perhaps the greatest scourge of all, there is the 
immense amount of chronic ill-health and actual disease caused or pro- 
moted by the unhealthy conditions found in our large cities, due to bad 
housing and overcrowding—the so-called diseases of environment. 
Malta Fever. 
But to return to the infectious diseases. After the living germs or 
parasites causing them had been isolated the process of prevention was 
soon begun. The methods employed were varied, and I may illustrate one 
of the simplest by relating briefly the history of the prevention of Malta 
fever, with which I was myself, to some extent, associated. 
Malta fever is really a widespread disease, although it is called by a 
local name. It is found all round the Mediterranean, throughout Africa as 
