358 INFECTION AND IMMUNITY 



complete and three-fourths saturation with ammonium sulphate. It 

 is interesting to note that these two fractions also incited antibodies, 

 by which precipitin and complement fixations could be obtained, a 

 matter which, in this case, is of considerable importance. For 

 further discussion of other claims of non-protein anaphylactic anti- 

 gens, we refer the reader to the article by Coca and the one by 

 Wells. We may summarize here by saying that, as far as we know 

 at the present time, anaphylactic antigens differ in no way from 

 other antigens, and that no substance at the present time has been 

 proven to be an anaphylactic antigen (in the sense in which we 

 define the term above), with which antibody formation in animals 

 has failed. In other words, any substance that can incite the forma- 

 tion of true antibodies may also be an anaphylactic antigen. 



THE METHODS OF SENSITIZATION. Experimental sensitization. may 

 be active or passive, and differs to some extent according to the 

 species of animal under observation. The early observations were 

 chiefly made on guinea pigs. Guinea pigs can be actively sensitized 

 by a single injection of various amount. When dealing with animal 

 sera such as horse serum quantities of anywhere from 0.1 to 1 c.c. 

 are most suitable. Minute amounts, however, will suffice, and 

 Rosenau and Anderson 23 succeeded in one case in sensitizing with 

 one one-millionth of c.c. of horse serum. If so sensitized, the animals 

 become hypersusceptible at varying periods, hardly ever in less than 

 six days, the ideal time for reinjection ranging between two and 

 three weeks, somewhat dependent upon the amount given. Various 

 statements have been made as to the relationship of the incubation 

 time and the initial dose given to guinea pigs. The ideal time for 

 injection is that at which the maximum amount of antibody has 

 been formed on the cells Avith the minimum amounts of circulating 

 antigen and antibody in the blood. The statement of Coca is prob- 

 ably right, that, in general, the small amounts injected into guinea 

 pigs require a relatively longer incubation period, but extremely 

 large amounts (5-10 c.c.) may have a similar effect. The method 

 of administration, to some extent, governs the incubation period 

 in the same way that it governs the speed of antibody formation. 

 However, the administration of the antigen to guinea pigs and other 

 animals may be carried out in any way, except by feeding, and 

 even feeding may result in a certain amount of hypersusceptibility 



23 Rosenau and Anderson, loc. cit. 





