INTRODUCTORY AND GENERAL 23 



by drying. The only practical example is rabies. There the 

 process of immunization is carried out by means of the use of a 

 series of vaccines of gradually increasing degrees of virulence, the 

 degree dependent on the time for which drying has gone on. It 

 is, of course, necessary to proceed with extreme caution, since the 

 cords that have been dried for but a few days are still infective 

 and virulent, and the amount of natural immunity in man is 

 extremely small, so that an attempt to accelerate the process 

 might be fatal. The method varies somewhat at different labora- 

 tories, but the following may be taken as a type of the procedure 

 used. It is of interest as being the method used in the first case 

 treated that of Joseph Meister. 



Day i. Inoculation with vaccine made by drying the cord for 

 fourteen days. A second injection with cord treated for ten 

 days. 



Day 2. Two injections ; cords dried for eleven and nine days. 



Day 3. One injection ; cord dried for eight days. 



Day 4. One injection ; cord dried for seven days. 



Day 5. One injection ; cord dried for six days. 



Day 6. One injection ; cord dried for five days. 



Day 7. One injection ; cord dried for four days. 



Day 8. One injection ; cord dried for three days. 



Day g. One injection ; cord dried for two days. 



Day 10. One injection ; cord from a rabbit which had died 

 the same day, and which was therefore unaltered in virulence. 



The method in use in France at the present day is almost like 

 this, except that the latter stages are repeated twice, or, in severe 

 cases, three times i.e., on the ninth and fourteenth days in mild 

 cases (and on the nineteenth also in severe ones) injections of 

 nine-day cords are started, and the strength increased rapidly, so 

 that three-day cords are used on the thirteenth, eighteenth, and 

 twenty-first. In Germany the treatment is begun with eight-day 

 cords, the older ones being considered inert. 



(c) By the injection of living cultures modified by heat. The 

 classical example is vaccination against anthrax by means of 

 Pasteur's two vaccines, the method of preparing which is given 

 on p. 1 8. The first vaccine is injected, and is followed by the 

 second in about a fortnight, immunity being established in about 

 another fortnight. 



(d) By the injection of cultures attenuated by prolonged cultiva- 

 tion in vitro. The use of this method in the case of chicken 



