MEMBRANE CHANGES DURING STIMULATION 371 



from the facts of passive sensitization, in which the 

 sensitized condition is produced in a normal guinea-pig 

 by injection of blood from another animal which has 

 already been immunized to the protein in question. 

 Passive sensitization can also be produced in vitro by 

 bathing strips of uterus with serum from an immunized 

 animal. The most probable interpretation of this 

 phenomenon is that the circulating anti-body is adsorbed 

 or fixed by contact with the smooth muscle cells, thus 

 becoming a constituent of the protoplasmic surface 

 layer. When the antigen (the original protein used for 

 immunization) is introduced, it reacts with the adsorbed 

 anti-body, and in so doing alters the structure or con- 

 sistency or permeabiHty of the surface layer (very much 

 as a specific cytolysin would do) in a manner corre- 

 sponding to strong stimulation. Contraction then 

 results; and since the antigen-anti-body reaction is an 

 irreversible one, the muscle cells remain firmly and 

 persistently contracted, with results fatal to the animal. 

 Dale has brought forward evidence that the specific 

 chemical interaction underlying anaphylactic shock is 

 identical with the precipitin reaction, the difference 

 being that the reaction occurs within the cell instead of 

 in the blood stream.^ If this is the case, it is easy to 

 understand why powerful stimulating effects should 

 result from precipitation of proteins within the proto- 

 plasmic surface-film, since such a process must alter 

 the structure and permeability of this layer and hence 

 act as a stimulating condition in the same manner as 

 any other cytolytic change would do. 



^ Dale, Croonian Lecture, Proceedings of the Royal Society, B, XCI 

 (1920), 126. 



