440 INFECTION AND RESISTANCE 



the localization, quantitative discharge of antigen, and consequent 

 production of antibodies is of necessity irregular and different in 

 each individual case. We have learned, as a general conception, 

 however, that the introduction into the animal body of antigenic sub- 

 stances of all varieties leads, under certain conditions, to increased 

 tolerance or resistance under other circumstances to a state of 

 greater susceptibility these diametrically opposed physiological 

 consequences being, in all probability, determined by relative concen- 

 trations of antigen and antibody, their speed of contact, and their 

 quantitative relationship to available alexin. The problems of clini- 

 cal medicine in which the possibility of anaphylaxis can be at all 

 considered, therefore, are extremely complicated, and few of them 

 can be approached by direct experiment. 



In the case of serum sickness the analogy has been so clear and 

 the experience with human beings so extensive that practically no 

 doubt can exist as to the common mechanism of this condition with 

 that of experimental anaphylaxis. In the other conditions men- 

 tioned the connection is one of great likelihood, but after all is in- 

 ferential, and calls for much further investigation. For this reason 

 it is best to abstain from a further enumeration of many other 

 maladies in which the condition of hypersusceptibility has been sug- 

 gested as a vaguely possible etiological factor. 



AND THE TUBERCULIN BEACTION 



There is one class of phenomena, however, which calls for 

 further discussion in this connection, since its dependence upon 

 anaphylaxis, while generally assumed, is still opposed by many 

 authorities. This consists of the various DIAGNOSTIC REACTIONS in 

 which extracts of micro-organisms are injected, or brought into con- 

 tact with the skin or conjunctiva of infected subjects. Such are the 

 various forms of the tuberculin reaction, the typhoid reaction of 

 Chantemesse, the one of Gay, and the luetin reaction of Nbguchi. In 

 the tuberculin reaction the conditions have been thoroughly studied, 

 and we may make a detailed consideration of this example serve to 

 bring out the general principles involved. 



In all forms of the TUBERCULIN REACTION there is a very evident 

 hypersusceptibility to various forms of antigen derived from the 

 bacillus. When the tuberculin is injected subcutaneously the reac- 

 tion is systemic and also localized to a certain extent in any tubercu- 

 lous foci which may be present. When the v. Pirquet or Moro skin 

 reactions are carried out, or the Calmette ophthalmic test is made, the 

 reactions are almost purely local. In all cases reactions are induced 

 by quantities of antigen which cause no effect whatever in normal 

 individuals. 



