PHYSIOLOGY AND BIOCHEMISTRY OF SHOCK 443 



In considering acetylcholine as a factor in anaphylaxis, it is true 

 that the nerve cells and heart muscle contain cholinesterase which 

 destroys acetylcholine. But there are regular intervals during which it 

 produces its effect. Apparently, this function is multiplied manifoldly 

 as a result of an abnormal degree of stimulation causing inhibitions of 

 normal functions. The specific role of histamine is likewise beset with 

 complications in view of the fact that it can be destroyed by specific 

 enzymes at the site of its liberation. 



The data concerning anaphylaxis which have been presented in 

 detail may perhaps lend themselves to systematization in the following 

 sequence: 



The interaction of antigen and antibody at the surfaces of 

 susceptible cells may cause displacement of lipid or protein components 

 of the cell surface membrane in such a way as to alter permeability 

 relations and otherwise disturb existing kinetic and chemical equilibria 

 within the cells. Such disturbances may initiate predominantly cata- 

 bolic action by proteolytic or other intracellular enzymes resulting 

 in liberation possibly primarily of acetylcholine and perhaps second- 

 arily of histamine. Abnormal concentrations of acetylcholine and hista- 

 mine in the circulation cause contraction of smooth muscle in the 

 respiratory and vascular systems, promote glandular secretion and 

 injure capillary endothelium, as well as produce their characteristic 

 effects through the sympathetic and parasympathetic nervous systems. 

 The impairment of respiration and of oxidation thus brought about 

 further increases capillary permeability and loss of fluid from the 

 circulation into the tissue spaces. The resultant anoxia further ag- 

 gravates the original cellular injury. 



