Vice-President’s Address. 137 
main point, however, I wish to point out here is the evidence 
that this affords that the antitoxic effect is really not the 
result of direct chemical changes between the toxin and the 
antitoxin leading to the destruction of the latter, and is not 
comparable to the neutralisation of an acid with an alkali 
producing a neutral substance. 
The next disease to which I shall refer is hydrophobia, 
This disease presents, so far, a peculiarity which is only 
shared by one other, for which there has been introduced a 
method of protective vaccination. The peculiarity is, that 
although the virus of the disease can be obtained, the microbe 
to which it must certainly be due has not been demonstrated, 
so that nothing whatever is known of it directly, only its 
products and its effects making its existence certain. The 
virus in this disease is present in its most concentrated state 
in the spinal cord, and it is by making an emulsion of that 
structure that the virus is obtained, mixed, of course, with 
the emulsified cord. This virus becomes weakened by 
exposure and drying of the cord, so that in the course of a 
few weeks it is entirely destroyed. As a consequence of this 
gradual attenuation of the virus, it can be obtained of any 
strength, and by inoculating animals first with a very weak 
virus, and then gradually increasing the strength, the animal 
so treated becomes refractory to the most powerful doses. 
This is a still further example of the different ways in 
which attenuation can be produced, and this is the first 
instance I have given you in which mere hanging in dry air 
has been sufficient to lead to attenuation. 
There is, however, still a further side to this, and which 
has bearings upon our general subject. If the blood-serum 
of an animal rendered immune be taken and mixed with the 
rabic virus, and left thus in contact with it, it has been 
found that the virus ultimately loses its power, and this is 
true whether the serum be taken from a vaccinated man or a 
vaccinated animal. The serum of a vaccinated animal may 
thus be used as a preventive vaccine; although the method 
appears to be inferior to Pasteur’s original method. 
Observations have lately been made upon the effect of the 
artificial digestion of this toxin, from which it appears that 
