HYPERSUSCEPTIBIL1TY 359 



under unusual or pathological conditions (abnormal permeability of 

 the intestinal mucosa). 



When sensitizing guinea pigs with bacterial proteins or pollen 

 and some other vegetable proteins, it is necessary to inject anywhere 

 from six to ten times on consecutive days, and testing about three 

 weeks after the last injection. 



In dogs active sensitization is hard to obtain by one injection. 

 Single doses of 2 to 3 c.c. of normal horse serum are usually followed 

 by sensitization in three weeks, at least such results seem to have 

 been obtained with some regularity by Simonds 24 and others. Such 

 sensitization, however, is not as acute and severe as that generally 

 observed in guinea pigs under similar conditions. Weil, 25 however, 

 obtained acute shock in dogs by giving two sensitizing injections 

 within a few days, and testing with large quantities of serum after 

 two and three weeks. 



Rabbits are difficult to sensitize with a single dose under any 

 circumstances, but may easily be sensitized by repeated injection. 



The lower monkeys are extremely difficult to sensitize under any 

 circumstances. 26 



Our knowledge of sensitization in man is of course based entirely 

 upon clinical observation. And it is held, especially by one inves- 

 tigator of anaphylaxis, that man cannot be sensitized. This, how- 

 ever, does not seem to us to be tenable, and anaphylaxis in man is 

 not an uncommon observation as manifested by serum sickness, im- 

 mediate skin reaction and accidents observed especially among 

 asthmatics treated with foreign protein for one or another clinical 

 reason. Fatal acute shock in man, however, is fortunately rare. 



PASSIVE SENSITIZATION. It is this phenomenon of passive sensi- 

 tization which has thrown the most important light upon the process. 

 It was first demonstrated by Nicolle, 27 by Otto, 28 and by Gay and 

 Southard, 29 all of whom showed that the hypersusceptible state 

 could be passively transferred to normal animals by injecting them 

 with the serum of anaphylactic animals. In such experiments the 

 serum of the anaphylactic animal is first injected in quantities of 



24 Simon ds, Jour. Infcc. Dis., 19, 1916. 



25 Weil, Jour. Tmmun., 2, 1917, 429. 



^7Ansser, Proc. Soc. Exper. Biol. and Med., 18, 1920, 57. 



27 Nicolle, Ann. de 1 'Inst. Past., 2, 1903. 



28 Otto, Munch, med. Woch., 1907. 



29 Gay and Southard, Jour. Med. Ees., May, 1907. 



