22 THE PRESIDENTIAL ADDRESS. 
This method of prevention, by the destruction of the louse, although 
doubtless requiring careful organisation and energy in carrying out, was 
shown before the end of the war to be a perfectly practicable proposition, 
and there can be little doubt that, if the war had lasted much longer, trench 
fever, like tetanus, would have practically disappeared. 
Besides the main discovery from the preventive point of view that the 
louse is the carrier, there are many other points of interest in the natural 
history of trench fever. 
The living germ causing it has never been recognised in the human blood 
or tissues, probably on account of its extreme minuteness, and its conse- 
quent liability to confusion with other small granules. 
But when the louse sucks blood from a trench-fever case there is 
apparently a great multiplication and development of the supposed 
micro-erganism. In five to nine days the louse becomes infective, and there 
is seen in the stomach and intestines enormous numbers of very minute 
bodies. What the exact nature of these bodies is, is unknown, but there 
ean be little doubt that they are the infecting agents by which the louse 
passes on the disease. They pass out in countless numbers in the droppings 
or excreta of the louse, and it is to these bodies in the excreta that infection 
is due. The louse seldom if ever gives rise to the disease in the act of biting. 
It is the infective excreta thrown out on the skin which causes the infection. 
‘The micro-organisms or so-called Rickettsia bodies contained in the 
excreta find their way into the blood through abrasions or scratches, and 
‘$0 give rise to the fever. ; 
From what has been said it will be seen that trench fever is an interest- 
ing disease. It also explains why it disappears in times of peace. As soon 
as the war was ended, and our men could leave the trenches and resume 
their normal habits, the disease disappeared. The louse was eliminated and 
the trench fever with it. 
Typhus Fever. 
Another disease of the undetermined group closely related to trench 
fever and also carried by the louse is typhus fever, one more of the furies 
following on the heels of war. The French and British Armies escaped this 
scourge to a great extent, but some of the other countries, such as Serbia, 
Bulgaria, and Poland, were not so fortunate. It is stated that 120,000 
Serbians died of this disease during the war, and it was only after vigorous 
steps had been taken in sanitary measures directed against the louse that 
the epidemic was got in hand. 
