256 Imniunity in Some of its Biochemical Aspccts [Jan. 



Explanat'wn of natural immimity. Ehrlich's views concerning 

 the necessity for fitting receptors in order that a microörganism may 

 attack the body cells afford a satisfactory explanation of the im- 

 munity possessed by certain animals against particular infections. 

 Thus, it is obvious that the entire absence of receptors fitting a cer- 

 tain microörganism renders the body immune against infection by 

 that microörganism. Moreover, the location of the receptors may 

 be responsible for the relative immunity of an animal under natural 

 conditions and its susceptibility when these conditions are changed. 

 Thus, if receptors for a particular poison are present both in a vital 

 tissue, like the brain, and in an indifferent tissue, like the muscles, 

 it is clear that while an intracerebral injection of the poison might 

 prove fatal, an intramuscular one might be almost without effect. 



Anaphylaxis. Most of you are probably familiär with the 

 work of Vaughan and Wheeler concerning the cleavage products of 

 proteins, and recall that some of their products were highly poison- 

 ous. Certain observations of the past few years indicate that, in the 

 parenteral digestion of proteins, similar cleavage products are pro- 

 duced. Historically this aspect of immunity may be said to date 

 from 1906, from the studies undertaken by Ehrlich's pupil, Otto, 

 and from experiments made about the same time in the U. S. Hy- 

 gienic Laboratory by Rosenau and Anderson. In the course of the 

 standardization of diphtheria antitoxin, it had been noted that 

 guinea pigs, which had previously been injected with toxin-antitoxin 

 mixtures, were often killed by a subsequent injection of horse 

 serum. When the subject was studied it was found that, when 

 an animal is injected with an allen protein, there develops after a 

 time a specific hypersusceptibility for this protein. After a definite 

 interval, if the animal is given a second injection of the same pro- 

 tein, violent Symptoms occur, which may end fatally. The reac- 

 tion is specific, so that animals sensitized, for example, to horse 

 serum, manifest little or no hypersusceptibility to other sera. It is 

 possible, however, to sensitize an animal to several proteins simul- 

 taneously. The sensitizing dose may be very small — even as little 

 as one-millionth of a cubic centimeter of horse serum has sufficed 

 to render a guinea-pig sensitive. A varying length of time must 

 elapse after the sensitizing injection before the animal becomes fully 



