VACCINE THERAPY IN THEORY AND PRACTICE 599 



before prophylactic inoculation was successfully carried out 

 against any other disease. So long as the infective agents 

 causing disease were unrecognised, experiments were quite 

 dependent upon chance for success, and all recent advance in 

 immunisation has depended upon a knowledge of bacteriology. 



The first great step in this direction was taken by Schwann, 

 who demonstrated that organic bodies do not undergo decom- 

 position except in the presence of micro-organisms. 1 This was 

 followed by the work of Pasteur on fermentation, and the identi- 

 fication of the yeast fungus as its cause, 2 in the year 1857. 



The probability that disease was caused by similar organisms 

 was by this time suspected ; indeed, in 1850 Davaine had observed 

 and described anthrax bacilli in the blood of animals with that 

 disease, 3 though he did not recognise them as the cause. In 

 i860 Delaford cultivated the bacteria in blood, and in 1863 Davaine 

 showed their constant presence in anthrax blood, and suggested 

 that the disease was due to them. By this time, then, a specific 

 organism had been shown to be constantly present in a certain 

 disease, and to be capable of cultivation outside the body. 



It still remained to obtain the organisms in pure culture, 

 which was first done by Koch in 1876, by growing them on a 

 solid medium. This work was confirmed and continued by 

 Pasteur; both these observers produced the disease in animals. 



In 1 88 1 Pasteur first used a vaccine made from attenuated 

 anthrax cultures, with which he successfully inoculated sheep. 

 The method of Jenner was thus repeated, employing an organism 

 whose relation to the disease against which prophylaxis was 

 sought was definitely known. The extension of this principle 

 to other diseases was now merely a matter of time. 



In 1885, after many experiments on animals, Pasteur inocu- 

 lated the first human patient against rabies. In this again no 

 organism had been isolated, but the virus had been traced to 

 the spinal cords of infected animals, and Pasteur employed 

 emulsions of such cords. Inoculations are used after a person 

 has been bitten by a possibly rabid animal, but only as a 

 prophylactic measure. The incubation period of rabies is a long 

 one— three weeks or more — and it is possible to confer an active 

 immunity before the infective agent reaches the spinal cord. 



1 Ehrlich, Croonian Lecture, Proc. Roy. Soc. vol. Ivi. 



2 Bosanquet, Serums, Vaccines and Toxines. 

 1 Bosanquet, op. cit. 



