ANAPHYLAXIS 151 



sensitizes an animal that a second injection after an interval 

 of about twelve days may cause the reaction known as anaphylac- 

 tic shock. The guinea pig is apparently the most susceptible of 

 all animals to horse serum, yet a first large dose gives rise to no 

 symptoms. A second injection of a minute amount may cause, 

 within five or ten minutes, a condition of restlessness and spasmodic 

 respirations and probably partial or complete paralysis. Recov- 

 ery may take place at this stage or convulsions may develop and 

 the guinea pig may die within twenty or thirty minutes. 



The symptoms of anaphylactic shock are not the same in all 

 animals, and this has been explained on the ground of slight dif- 

 ferences in anatomical structure. It has been demonstrated 

 that smooth muscle cells are the most hypersensitive. In the 

 case of the guinea pig the mucosa of the bronchi is relatively 

 thick compared with the lumen and the muscular contraction 

 throws it into folds, with the result that the guinea pig is asphyxi- 

 ated. The bronchi of dogs have relatively less smooth muscular 

 tissue. This probably accounts for the few cases of death from 

 asphyxia in anaphylactic dogs. In the latter contraction of the 

 smooth muscle of the intestines starts a vigorous peristalsis ; the 

 muscles of the heart and arteries are also affected. 



Fortunately the severe and fatal forms of anaphylaxis are ex- 

 tremely rare in man ; most cases have occurred in persons known 

 to be susceptible to horse protein. This undue hypersusceptibility 

 is revealed by the asthmatic attacks which such a person exhibits 

 when entering a stable or nearing a horse. Serum anaphylaxis 

 or " serum sickness " in man sometimes occurs following a dose 

 of antitoxic serum ; the characteristic symptoms are a skin erup- 

 tion, swelling of the lymph glands, joint pains, and albuminuria. 

 These symptoms are altogether independent of the antitoxin con- 

 tained in the serum and are purely dependent on the serum as 

 such. For this reason a concentrated antitoxin is less likely to pro- 

 duce serum sickness. In the majority of cases symptoms do not 

 appear for from eight to ten days. Presumably an amount of the 

 antibody or protein splitting substance has been generated by that 

 time and all of the horse serum that remains in the circulation 



