IMMUNITY AND SUSCEPTIBILITY 685 



proteins of the bacterial cells have been shown to act in the same way. 

 Animals injected, as described above, may be rendered hypersusceptible 

 to all bacterial proteins. Furthermore, as referred to above, individuals 

 may be naturally hypersusceptible to bacterial and other proteins. 

 The manner of the original sensitization in these cases is not known. 

 Sensitization which has been either naturally or artificially acquired 

 is transferred in most instances in utero to the first generation; that is, 

 a mother may be sensitized, convey the sensitizing substances to her 

 young while in the uterus, and when these offsprings are subsequently 

 injected after birth with the same protein they may be intoxicated or 

 killed. In this connection it should be stated that the so-called in- 

 herited tendency to specific diseases may be something more definite 

 than we are ordinarily accustomed to regard it. Suppose a mother 

 becomes tuberculous and is, therefore, sensitized to the proteins of Bact. 

 tuberculosis; it is quite possible for her to convey to the offspring this 

 susceptibility to the particular proteins of Bact. tuberculosis as has been 

 demonstrated artificially. After birth, or in later life, when the causal 

 microorganisms of tuberculosis are taken into the body, as they are in 

 about ninety-five per cent of all persons in civilized countries, the 

 bacteria may find a more than ordinarily susceptible individual and 

 may develop with comparatively little hindrance. If this condition 

 be true naturally as it is when produced experimentally in suscep- 

 tible animals a very interesting and scientific explanation of the 

 so-called inherited tendency to tuberculosis is at hand. 



PREDISPOSITION' AND NON-INHERITANCE or INFECTIOUS DISEASES. 

 There is probably no such thing as a truly inherited infectious disease. 

 This point has been debated and discussed for a great many years and 

 the above conclusion has been reached by the majority of investigators. 

 By inheritance is meant the transference of a property, or in this in- 

 stance, a pathogenic microorganism by the nuclear substance of either 

 the spermatozoon or the ovum. It is only the nuclear substances which 

 combine to form the new individual. It is true among certain of the 

 lower animals, such as the fowls and some insects, that microorganisms 

 are carried within the egg but the eggs are quite different in structure 

 from the human or mammalian ovum. The egg of the above-mentioned 

 animals is composed largely of yolk-furnishing food and there is ample 

 opportunity for microbic growth, while the mammalian ovum contains 

 no yolk. Such instances should be referred to as germ-cell transmission, 



