Vice-President’s Address. 135 
temperature a quantity of the blood taken from an animal 
dead of the affection, to inject small quantities of it, and to 
repeat the injections many times. These measures rendered 
the animal entirely immune to the fatal virus. Not only was 
this the case, but the blood of the animal so vaccinated 
exercised a preventive power when inoculated into others. 
At the same time it was shown, that, notwithstanding this 
preventive faculty, the blood-serum had no bactericide or 
antitoxic qualities, strictly so called. 
This effect of heat at a certain limit in attenuating virus 
is extensively applicable, but there are other methods, also 
used successfully, to which I must refer, and it will make 
the subject more interesting if 1 illustrate some of these by 
reference to well-known diseases. 
I may take diphtheria first, a disease due to a bacillus 
which develops at the seat of invasion, that being most 
commonly the throat. The bacillus is confined to the locality 
where it has become implanted, and does not become diffused 
throughout the body. It produces a toxin, to the absorp- 
tion of which most of the symptoms are due. Here, as in 
other cases where the microbe is cultivated separately, it can 
be filtered out of the fluid which contains its toxin. This 
toxin can be produced of an extreme degree of virulence, 
and all the animals usually used for investigation, such as 
the rabbit, guinea-pig, dog, etc., are susceptible to it. Owing 
to this, there was considerable difficulty in working out a 
satisfactory method of preventive inoculation. It was found 
that the virus might be attenuated in various ways, and 
these it is unnecessary to dwell upon in detail; one of them, 
however, I must mention; it is this, that if the fluid con- 
taining the toxin were mixed with a quantity of a solution 
of iodine, an animal withstood a dose of the virus, thus 
mixed, that would by itself have proved fatal. By repeated 
injections of this mixture the animal was rendered immune 
to the diphtheria bacillus or its toxin. 
You must always remember that the ultimate object of all 
these investigations is to find a method of inoculation which 
will be applicable to man, and the investigation of diphtheria 
had very markedly this for its object. 
