"REACTIONS" AND SIMILAR PHENOMENA 311 



organs which often follows the action of poison. The kidneys, 

 etc., excrete the substance, but in doing so are injured, and a 

 smaller dose of the poison may now produce a great effect, since 

 it cannot readily be eliminated. 



The main objection to this theory is that it is difficult to 

 imagine such a selective destruction of the receptors as seems 

 necessary to account for the fact that the hypersensitiveness is 

 specific. We should expect the creeping necrosis or interference 

 with nutrition to act more generally, so that an animal highly 

 sensitized to one toxin would show some degree of sensitiveness 

 to others. It seems also inadequate to explain the facts of serum 

 anaphylaxis, which will now be described, since here the animal 

 is sensitized with minute amounts of a substance which causes no 

 toxic symptoms in comparatively enormous doses in a normal 

 animal. Here the anaphylaxis appears to be the production of a 

 new sensitiveness rather than the exaltation of one previously 

 existing. 



There are two of these phenomena of hypersensitiveness to 

 serum Arthus' phenomenon and Theobald Smith's phenomenon, 

 both of which are referred to as " serum anaphylaxis." The latter 

 is the more important. 



Arthus' phenomenon appears when a guinea-pig receives 

 several injections, at intervals of a few days, of normal horse 

 serum, a substance which in itself is scarcely more toxic than 

 normal solution. After a few such inoculations the animal becomes 

 hypersensitive, or anaphylactized, and after another injection an 

 cedematous mass, an aseptic abscess, or an area of necrosis, 

 appears at the site of a new inoculation, which need not be in a 

 region in which a previous injection has been made ; the altera- 

 tion is a general, and not a local, one. After several of these 

 injections the animal becomes cachectic, and dies after several 

 weeks. An animal thus sensitized will die rapidly after the 

 injection of 2 c.c. of serum into the veins. 



It should be noticed that these results are not due to the accu- 

 mulation of the horse serum in the system, since they may be 

 brought about by the injection in divided doses of an amount 

 which an animal can stand with impunity if given in a single 

 dose. 



Theobald Smith's phenomenon occurs when an animal has been 

 sensitized by a very small injection of horse serum ( T J^ c.c., or 

 even as little as T^nro^nnr c>Ct ' an almost inconceivably small 



