PROTECTIVE INOCULATIONS. 275 
On June 13th, 1881, Pasteur communicated the results of his famous 
experiment at Pouilly-le-Fort, near Melun. He says: 
‘On the 5th of May, 1881, we inoculated, by means of a Pravez syringe, 
twenty-four sheep, one goat, and six cows, each animal with five drops of 
an attenuated culture of the anthrax bacillus. On the 17th of May we rein- 
oculated these animals with a second virus, also attenuated, but more virulent 
than the first. 
‘On the 31st of May we proceeded to make a very virulent inoculation in 
order to test the efficacy of the preventive inoculations made on the 5th and 
17th of May. For this experiment we inoculated the vaccinated animals, 
and also twenty-four sheep, one goat, and four cows which had not received 
any previous treatment. 
‘“‘The very virulent virus used on the 31st of May was obtained from 
spores preserved in my laboratory since the 21st of March, 1877. 
‘‘In order to make the experiments more comparable we inoculated alter- 
nately a vaccinated and a non-vaccinated animal. When the operation was 
finished all of those present were invited to reassemble on June 2d, 7.e., 
forty-eight hours after the virulent inoculation was made. 
‘‘Upon the arrival of the visitors on June 2d, all were astonished at the 
result. The twenty-four sheep, the goat, and the six cows which had received 
the attenuated virus, all presented the appearance of health. On the con: 
trary, twenty of the sheep, and the goat, which had not been vaccinated, were 
already dead of anthrax ; two more of the non-vaccinated sheep died before 
the eyes of the spectators, and the last of the series expired before the end of 
the day. The non-vaccinated cows were not dead. We had previously 
proved that cows are less subject than sheep to die of anthrax. But all had 
an extensive cedema at the point of inoculation, behind the shoulder. Cer- 
tain of these cedematous swellings increased during the following days to such 
dimensions that they contained several litres of liquid, deforming the animal. 
One of them even nearly touched the earth. The temperature of these cows 
was elevated 3° C. The vaccinated cows did not experience any elevation of 
temperature, or tumefaction, or the slightest loss of appetite. The success, 
therefore, was as complete for the cows as for the sheep.” 
The facts that infection depends to some extent upon the number 
of bacilli introduced, and that animals which have a certain degree of 
immunity, like the Algerian race of sheep, may succumb when they 
are inoculated with a certain quantity of virus, although they resist 
asmaller amount, were announced by Chauveau in his communication 
to the French Academy at the séance of June 28th, 1880. He says: 
“The facts which I have just presented show that the anthrax bacillus 
behaves in the organism of Algerian sheep, not as if it were deprived of the 
principles necessary for its development, but rather as if it were in a medium 
rendered unsuitable for its growth by the presence of substances injurious to 
it. In avery small number the bacilli are arrested in their development by 
the inhibitory influence of these substances. When they are very numerous, 
on the contrary, they surmount more easily this obstacle to their prolifera- 
tion.” 
This quotation shows that Chauveau had at this early date arrived 
at an explanation of immunity very nearly in accord with that which 
is now generally accepted. 
The fact that infection is influenced by the quantity of the infec- 
