1913] Charles Frederick Boldnan 249 



bacteria with which the original attack was produced. Subse- 

 quently Salmon and Smith, in this country, showed that it was not 

 necessary to produce even a mild attack of the disease by injecting 

 living germs, but that the injection of dead germs would produce an 

 immunity against that particiliar infection. 



Specificity of acquired immunity. Acquired immunity, whether 

 caused by a previous natural attack of the disease, or artificially by 

 the inoculation of living or dead germs, is always strictly specific; 

 that is, the protection extends only to the particular disease which 

 has previously occurred or against germs of the kind previously 

 injected. An attack of scarlet fever protects only against scarlet 

 fever but not against measles. Inoculating an individual with ty- 

 phoid bacilli protects him only against typhoid fever, but not against 

 dysentery, plague or cholera. This acquired immunity is often 

 transmitted from mother to offspring, transmission being effected 

 mainly, according to Famulener, through the Colostrum. 



Additional natural defenses against DISEASE. Beforc ex- 

 amining into the nature of specific acquired immunity, let me call 

 attention to certain important means by which the body is protected 

 against infectious diseases in general. Many of these means are 

 so commonplace that their significance is often overlooked. 



The protection afforded by the unbroken skin is undoubtedly one 

 of the most important means of defense. A similar protection, 

 though less effective, is afforded by intact and healthy mucous mem- 

 branes. The acid gastric juice undoubtedly destroys large numbers 

 of swallowed germs. It has been found that fresh blood serum is 

 able to kill a considerable number of germs, and this is therefore 

 another mode of defense. The white blood cells (leucocytes) 

 appear to be designed especially to destroy invading micröorganisms. 

 These cells take hold of, or rather engulf, the germs and digest 

 them. Still another mode of defense is seen in what takes place in 

 abscesses. When these are examined, it is found that the body has 

 built a wall of cells around the infected area, thus shutting off the 

 germs and their poisonous products from the rest of the body. 

 Finally, mention may be made of the collection of fluid, i. e., of 

 serum, as perhaps a means designed to dilute irritant poisons (pleu- 

 risy, Peritonitis). 



