Explanation of Immunity 105 



horse-serum into guinea-pigs, the intervals being too short to permit 

 anaphylaxis, antianaphylactin could be prepared. It seems difficult, 

 however, to imagine how such a substance could remain in the blood 

 throughout the entire subsequent life of the animal. 



Vaughan has endeavored to explain anaphylaxis by assum- 

 ing that when the strange protein in the blood reaches the cells 

 it is slowly broken down by enzymic action, but that the cells, 

 having once acquired the property of destroying it, seize eagerly 

 upon the protein the next time it is offered, disintegrate it rapidly, 

 and so disseminate throughout the body the degradation products, 

 some of which may be toxic and account for the reaction. 



Anaphylaxis is not a disturbance of the cells of the body, as 

 some have thought, but is at least in part a disturbance of the 

 composition of the blood, as can be shown by the occurrence of 

 what is known as passive anaphylaxis. If the blood-serum of a 

 sensitized animal be withdrawn and injected into a normal animal 

 of the same kind, it carries the sensitization with it. The new 

 animal, however, does not become sensitized at once, but only 

 after some days, hence it is equally true that the disturbance is 

 not solely in the blood, else why should not the sensitization be 

 immediately present upon the injection of the serum? 



Anaphylaxis may, furthermore, be local. Thus, when certain 

 substances like tuberculin are dropped in the eye there is no effect, 

 but when a second apphcation is made, after some weeks, the eye 

 may be reddened. 



Anaphylaxis may play a r61e in infection. In cases where an 

 attack of an infectious disease leaves no immunity, the body may 

 be left hypersensitive to subsequent attacks. 



EXPLANATION OF IMMUNITY 



Before the facts now at our disposal had been gathered together, 

 and before the phenomena of immunity against infection had been 

 compared with those of intoxication, Pasteur* and Klebsf en- 

 deavored to explain acquired immunity by supposing that micro- 

 organisms living in the infected animal used up some substance 

 essential to their existence, and so died out, leaving the soil unfit 

 for further occupation. This was known as the "exhaustion 

 theory." Wernichf and Chauveau§ thought it more probable 

 that the micro-organisms after having lived in the body left 

 behind them some substance inimical to their further existence. 

 This was known as the "retention theory." These hypotheses are 

 of historic interest only, and deserve no more than passing men- 

 tion, as they both fail to explain natural immunity or immunity 

 against intoxication. 



* "Compte rendu de la Soc. de Biol, de Paris," xci. 



t "Arch. f. experimentelle Path. u. Pharmak.," xni. 



t "Virchow's Archives," Bd. Lxxvm. 



§ " Compte rendu de la Soc. de Biol, de Paris," xc and xci. 



