TEXT-BOOK OF BACTERIOLOGY. 141 



Yet how necessary is reserve of opinion in this matter, has been 

 shown by the experiments of Koch and his collaborators, Gaffky 

 and Loftier, with regard to anthrax. They also found it possible, 

 by subcutaneous inoculation with attenuated bacilli, to make ani- 

 mals capable of withstanding an after-inoculation with cultures of 

 the highest degree of virulence. But they remarked, at the same 

 time, that this experiment did not by any means succeed equally with 

 every kind of animal, and, further, that even in the most success- 

 ful case a full security against all attacks of anthrax disease was 

 not obtained. As we shall yet see, the animals, when infected 

 under natural conditions, usually received the virus along with 

 their food and in the alimentary passags. Material containing 

 spores goes through the stomach without the destruction of the 

 spores, into the intestines, and thence the bacteria spread to other 

 parts. Against this kind of infection the inoculation grants no 

 unconditional and reliable protection, so that the animals sometimes 

 die of anthrax in spite of the inoculation. 



If this be placed along with the already-mentioned fact that 

 the vaccination itself, particularly with the stronger second virus, 

 sometimes ends fatally, it is natural that opinions are divided as to 

 the practical value of protective inoculation. This is a question of 

 utility which can only be decided by means of statistics, and statis- 

 tics show that for anthrax the use of protective inoculation is 

 desirable in countries or districts in which this disease occurs regu- 

 larly and spreads widely. Experience has also shown that this 

 inoculation yields better results with cattle than with sheep a fact 

 which deserves due attention. 



In the case of swine-erysipelas and chicken-cholera, the success 

 has not as yet been very satisfactory, and qualified advisers, there- 

 fore, pronounce against the use of inoculation as a protection 

 against these complaints. In the case of symptomatic anthrax, cat- 

 tle-doctors pronounce with one voice in favor of inoculation, which 

 may be regarded as a useful and effectual means of protection. 



But these purely practical considerations do not touch the heart 

 of the question, and do not invalidate the very important scientific 

 fact that under some circumstances the most virulent matter 

 may be rendered ineffectual by inoculation with attenuated virus. 



It may be readily supposed that for a phenomenon so extremely 

 striking and important, causes and explanations have been sought. 

 Yet in spite of the most persevering efforts which of late have 

 almost exclusively occupied the attention of investigators, no cer- 

 tain result has hitherto been attained, and to the question as to 

 how the acquired immunity is brought about, we are still unable to 

 give a decided answer. 



