128 IMMUNITY, NATURAL AND ACQUIRED 



septic conditions due solely to staphylococci or to mixed in- 

 fections of streptococci and staphylococci. 



Anti-typhoid, anti-cholera, anti-pneumonic, anti-plague, 

 and other sera are all prepared in an a.nalogous manner, and 

 have given in some instances valuable results. The only one 

 of which we have any experience is the anti-plague serum, and 

 we have had ample opportunities of witnessing its effects, 

 sometimes; magical, in cases of bubonic plague. 



Another example is the anti-rabic serum introduced by 

 Tizzoni and Pasteur, where conspicuous success has followed 

 the use of this serum in persons bitten by rabid animals in whom 

 hydrophobia would otherwise have developed. 



To quote Kanthack : " There is a striking difference, how- 

 ever, between immunity produced by inoculation of the bacteria 

 themselves and their toxins, whether attenuated or not, and 

 immunity produced by serum injections. In the former case the 

 animal gains its immunity after an active struggle with the 

 disease or 1( sions following the injection or intoxication ; in the 

 latter case there is no struggle with disease and no reaction ; the 

 animal remains passive while the immunity-conferring substance 

 is applied to its tissues. On account of this essential difference, 

 Ehrlich distinguishes active from passive immunity. Passive 

 immunity is effected quickly, is less persistent, and varies with 

 the amount of the serum used and with the degree of the 

 immunity of the animal which supplies the serum. Active 

 immunity, on the other hand, does not appear for days, not 

 until the animal has passed through the reactive stage ; then it 

 becomes permanent, and is proportional to the intensity of the 

 reaction rather than to the amount of vaccine used." 



Lastly we come to the subject of Natural Immunity, which 

 I will treat very briefly. I would call your attention tc two 

 facts — (1) that there are a large number of bacteria — the so- 

 called non-pathogenic bacteria, which, when introduced into an 

 animal, cause no symptoms, unites- perhaps in very large doses, 

 showing that the tissues and fluids of the animal body possess 

 a bactericidal action against germs of low virulence ; (2) that 

 there are other bacteria, which are very virulent to some species 

 of animals and harmless against others — anthrax, for example, 

 fowls immune to tetanus, goats to tubercle, c.p., natural resis- 

 tance to morphia in birds. This immunity must be due to a 

 special power on the part of that animal of destroying the germ 



