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PRINCIPLES OF GENERAL PHYSIOLOGY 



the sheep, cat, rabbit, dog, or man, nor to egg-white, but a powerful contraction to 

 a similar dose of horse serum, the antigen itself. 



Now, there are two points to be cleared out of the way before we proceed. 

 Fresh serum of all animals contains a toxic substance, which causes contraction of 

 smooth muscle ; this property diminishes considerably as the serum is kept and 

 has nothing to do with the anaphylactic reaction. A much larger dose has to be 

 given ; but, in the testing of the anaphylactic phenomenon, the fact must be 

 remembered. The curves of Fig. 258 show that the doses given have no effect 

 of this kind. Secondly, it might be supposed that the normal guinea-pig uterus 

 is particularly sensitive to horse serum, as compared with other sera. This is 



FIG. 258. ANAPHYLAXIS IN EXCISED UTERUS OF 

 ' GUINEA-PIG. 



Sensitised with 4 '.,-.' h c.c. horse serum. 



A, O'l c.c. sheep serum. 

 /.'. cat serum. 



C, rabbit serum. 



D, dog serum. 



E, human serum. 



F, egg-white. 

 O, horse serum. 



Powerful contraction with the antigen serum, but with no other 

 serum nor with egg-white. 



(Dale, 1912, Fig. 26.) 



found not to be the case ; a dose of horse serum, just as large as that of any other 

 serum, is required to cause contraction of the normal uterus. 



Although the specificity of the reaction appears to be so great, and is, in fact, 

 under proper conditions, sufficiently so to serve as a delicate test for the antigen, 

 there are some facts which show that it is really only of a quantitative nature, and 

 also that the phenomena of specific immunisation share this characteristic. Dale 

 finds (p. 188) that if the guinea-pigs are sensitised simultaneously to horse serum, 

 sheep serum, and egg-white, as can be done, the sensitiveness to horse serum, 

 although present, is comparatively low. To understand the further evidence, we 

 must consider the fact of desensitisation. Suppose a uterus, sensitive to horse 

 serum, has been tested with a fairly large dose and has given a powerful contrac- 

 tion, it is found to be incapable of response to a second dose. It is evident that 

 some kind of reaction has taken place between the sensitised tissue and the antigen, 



