142 TEXT-BOOK OF BACTERIOLOGY. 



Before discussing the various, and often contradictory, views 

 held by different authorities, let us state the simple facts, such as 

 they are. As just mentioned, it is possible to fortify animals, by 

 inoculating them with attenuated anthrax bacilli, against the 

 virulent bacteria. Bitter has shown that the thus inoculated bacilli 

 develop only in the immediate neighborhood of the spot where the 

 inoculation took place, and are not carried into other organs by the 

 circulating blood. Hueppe and Wood found that a species of bac- 

 teria, clearly distinct from the anthrax bacillus, apparently innoc- 

 uous and strictly saprophytic, was able to secure even very sus- 

 ceptible animals, such as mice and Guinea-pigs, against anthrax. 

 Roux and Chamberland found that cultures of virulent bacteria 

 freed from all micro-organisms and the tissue-juices of killed ani- 

 mals yielded protection against anthrax and a number of other 

 diseases. Before and after these investigators, Salmon and Smith, 

 Beumer and Peiper, as well as several others, have observed simi- 

 lar facts in regard to swine-fever, typhus, etc. Foa and Bonome 

 successfully employed upon the proteus a definite chemical sub- 

 stance which they supposed to be excreted in large quantities by 

 these micro-organisms, instead of using the real excretions, and 

 Wooldridge was even able to obtain immunity from anthrax by 

 means of a substance which has no connection with the vital 

 process of the bacteria, viz., by means of albumin from the tis- 

 sues, peculiarly changed and prepared. 



How can all these so apparently contradictory facts be har- 

 monized with each other ? Only, it would seem, by drawing the 

 conclusion that the immunity is brought about, not by the micro- 

 organisms themselves, but by certain chemical substances which are, 

 for the most part, bacterial products. These substances are produced 

 within the animal, at the place of inoculation, by the attenuated 

 bacteria in continually-increasing quantities, and spread through- 

 out the body. They are also contained in the cultures of virulent 

 bacteria and in the serous fluids, which — for example, in malignant 

 oedema — develop in the subcutaneous cellular tissue of the infected 

 animals. If we inoculate with such matter, but without special 

 precautions, we obtain no success with infectious species, because 

 live germs begin to grow in the new individual, and bring death, 

 m stead of protection, from disease. But if we remove the micro- 

 organisms by careful filtration or cautious application of heat, 

 their excretions remain, which do not multiply in the animal, but, 

 on the contrary, are diluted by mixture with the blood and the tis- 

 sue-juices, and their effects being thus diminished, they are able to 

 produce immunity. 



