PRESIDENT’S ADDRESS—SECTION I. 147 
longer or shorter period. This period varies greatly in different 
diseases, being of life-long duration in some, and comparatively 
short in others. As soon as the science of bacteriology had 
attained sufficient exactness, the problem as to the nature of 
this immunity from a recurrence of the same disease was at once 
attacked. It was gradually made clear that the symptoms of 
the disease are due mainly to the action of some poison or 
poisons called toxins, whicli the specific agents of disease 
(bacteria) manufacture in the blood or tissue fluids. If re- 
covery takes place, it can only be by the escape of the poisons 
from the body, before their action has become too destructive, 
or by the formation of some counter poison or antidote. That 
the cessation of symptoms and consequent recovery are due 
largely, and in the first instance, to this formation of a counter- 
poison or anti-toxin, has now been clearly shown. But is it 
necessary to wait for the natural formation of this antidote, 
while meantime the patient is in danger of dying, because the 
antidote comes too late? And in diphtheria, where the mor- 
tality, on the average, readily amounted to 25 or even 50 per 
cent., it is apparent that the natural process of cure was apt’ 
to be too late in coming about. But as the anti-toxin was 
shown to remain in the blood for some time after recovery, the 
question was the very practical one of using this stock of anti- 
dote for preventive or curative purposes by borrowing it from 
one person or animal for the relief of another. It would be 
manifestly inconvenient, if not impracticable, to trust to supplies 
from persons who had just recovered from an attack. But it was 
shown that some animals, by repeated inoculations or injections 
of the germs of the disease or of their poisons, were capable of 
producing the antidote. Much skill and labour were needed in 
selecting the most suitable animals for the purpose, and for 
securing safety in the use of the material obtained. The blood 
serum, containing the counter-poison, was first tried sufficiently 
on animals, and when this had been done, the technical diffi- 
culties were at an end. ‘This antidote is now used, and if 
sceptics have not been finally silenced, evidence of its 
efficacy, satisfactory to the vast majority of observers, has been 
supplied. The good results in the way of cure have been shown 
to depend chiefly on the promptness with which the remedy is 
applied, and, of course, on its quality, and the sufficiency of the 
dose. Anti-toxin is used, too, not only as a curative, but as a 
protective. Children in a family in which the disease has 
occurred may, by this system of inoculation, be guarded against 
the liability to attack during the exposure to infection. We are 
looking forward to the time, which can hardly be far distant, 
when others of the epidemic diseases which are now the scourge 
of humanity will, by similar methods, and by the application 
of similar principles, be rendered as harmless as small-pox now 
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