374 BACTERIA. 



twenty hours and the temperature is then raised to 47° C, for a period of 

 three hours. This is the second vaccine. The first vaccine is a culture 

 made from one that has been heated for three hours at 47° C. ; this is 

 incubated for from five to seven days at 35° to 37° C, and then for one 

 hour at 80°. Of these vaccines two drops are used for inoculating a sheep 

 and four for cattle, the animals being injected, cattle on the outer aspect of 

 the ear, sheep inside the thigh. The great drawback associated with the 

 use of vaccine so prepared is that it cannot be preserved for any length of 

 time, as under cultivation the original virulence is regained at once. 



Pasteur's classical experiments made in May 1881 gave 

 abundant evidence of the utility of this method of treat- 

 ment. On the 5th of May, twenty-four sheep, one goat, 

 and six cows were inoculated with a protective vaccine ; 

 twelve days afterwards they were again inoculated with a 

 somewhat stronger vaccine than that at first used, and on 

 the 31st of May these animals that had already been vac- 

 cinated, and twenty-four sheep, one goat, and four cattle 

 that had not previously been inoculated with the protective 

 virus, were injected with material from a virulent anthrax 

 culture. 



On the 2nd of June all the animals that had been 

 protected were found in apparent health ; of the others, 

 twenty-one sheep and the goat were dead, two other sheep 

 were dying, and the other was attacked later in the day. 

 The non-vaccinated cows were not dead, but they had all 

 marked local symptoms. Next day one of the vaccinated 

 sheep died, but its death was said not to be due to anthrax. 

 The experiment was repeated in a modified form by injecting 

 a quantity of blood and spleen pulp from a sheep that had 

 died of anthrax into sixteen non-vaccinated animals, and 

 into nineteen protected animals, with the result that on the 

 third day all the unprotected animals but one had succumbed, 

 whilst the others remained apparently healthy. 



Equally good results were not always obtained by other experimenters, 

 but in some cases, at any rate, the experiments appear to have failed 

 through want of attention to detail rather than from any defect in the 

 method itself, and from the failure to recognize that the initial virus is not 

 always of the same strength, that different animals have very different 

 degrees of susceptibility and natural immunity, and that the quantity of 

 the virus injected very materially alters the conditions of the experiments. 

 No tissues can be expected to cope equally well with large and with 

 small doses. 



A number of other methods of preparing a less virulent (or vaccine) 

 material have been described by different observers. Thus Toussaint 



