142 TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
One difficulty Pasteur had to contend with was to find the 
period of incubation of the poison. Every one knows the story 
of the Duke of Kichmond, who was bitten by a tame fox, and 
who died of hydrophobia two years afterwards. Instances in 
which the disease has developed itself in two or more months are 
common. Here again there is an agreement with what Watson 
Cheyne has found in his experiments on the disease produced 
by a special bacillus in the mouse. It is necessary to have a 
sufficient quantity of the poison, so to speak, to create the disease. 
One would have imagined that that would not matter, as the 
bacilli multiply so rapidly, but it is not so ; at any rate in certain 
cases. If a large quantity of the saliva entered, the incubation 
would be short ; if a small quantity, it might become localised 
and wither away, or it might, on a more favourable soil, slowly 
and surely work its way, and develop into madness later on. 
Pasteur found, however, that by inoculating rabbits direct 
into the brain, with the spinal marrow of an ordinary mad dog, 
the disease was generally fatal on the fifteenth day; and, as 
before stated, by carrying the inoculation on from one rabbit to 
another the period of incubation was shortened to seven days. 
The official French commission appointed to investigate the 
truth of this, reported that twenty-three vaccinated dogs (i.e., 
vaccinated with the attenuated virus before referred to) were 
bitten by ordinary mad dogs, arid that not one of them had taken 
rabies ; on the other hand, sixty-six per cent, of dogs bitten without 
being previously vaccinated took the disease. 
In July, 1885, Pasteur first began to try the effect of inoculating 
persons to prevent hydrophobia developing, after they were bitten. 
A boy named Joseph Meister, who had been bitten severely, was 
brought up from Alsace. It was pretty clear he could not escape 
being attacked by hydrophobia ; his mother had heard of Pasteur 
saving dogs, so she had faith that he could save human beings. 
By suspending the spinal cord of a rabbit, which had died of 
rabies, in pure air for fifteen days, the poison was lessened. The 
boy was first inoculated with this virus, and then on each succes- 
sive day for ten days with virus of greater intensity, until at last 
he was inoculated with virus of one day old. By experiments 
on rabbits it was found that the virus used up to the six days 
old from the fifteen days old, was not virulent, but that from the 
six days old up to one day was increasingly so. 
