492 IMMUNOLOGY 



the exi)losive edema of the liver that is observed in canine 

 anaphylaxis. Since cells lining the liver sinusoids belong to the 

 reticnlo-endothelial system, it has been suggested that the explosive, 

 hepatic edema points to these cells and the hepatic parenchyma 

 as the primary site of anaphylaxis. On the other hand, Wells 

 (1929) calls attention to evidence which indicates that the primary 

 site of the antigen-antibody reaction is upon or within the cells of 

 nonstriated muscle tissue. The evidence may be summarized as 

 follows : 



1. Smooth muscle removed from the body of sensitized guinea 

 pigs will give specific anaphylactic contractions when nontoxic 

 doses of the antigen used in sensitization arc added to the bath. 

 Desensitization can be demonstrated. 



2. The iuflalion of the lungs of the guinea pig, which is the 

 cliaract eristic i)lienomenon of ana])]iylaxis in that animal, is due 

 to the tetanic contraction of the smooth muscle of the secondary 

 and tertiary 1)ronchioles. 



3. Simonds has shown that the walls of the hepatic veins of the 

 dog are endowed witli a large amount of smooth muscle. He offers 

 experimental evidence which indicates that the characteristic drop 

 in arterial blood pressure results from the increased pressure in 

 the hepatic veins due to the tetanic contraction of the smooth 

 muscle in their walls. 



4. It luis been estaljlished by Coca and others that the most 

 important physiological anaphylactic phenomenon in the sensi- 

 tized rabbit is a tetanic contraction of nonstriated muscle present 

 in the walls of the pulmonary artery. 



Mechanisms of the Reaction. — While it is definitely estab- 

 lished that anapliylactic shock is due to an antigen-antibody re- 

 action occurring upon or within ti.ssue cells of tlie body, the exact 

 mechanism which elicits the physiological responses is unknown. 

 At the present time there are two theories either of which ap- 

 pears to offer an adequate explanation of most of the observed 

 phenomena. One theory assumes that the toxic stimulus results 

 from physical (colloidal) changes, either at the surface or within 

 the tissue cells, which result from antigen-antibody union. This 

 explanation is either a part of or implied by the physical theory 

 of Weil, the membrane hypothesis of Doerr, and the inflammation 

 theory of Opie. A second theory formulated by Lewis and sup- 



