PARENTERAL DIGESTION 67 



or may be brought into existence. However, it 

 should be stated that the present view does not 

 exclude the necessity of regarding protein di- 

 gestion in the blood as, in some instances at 

 least, specific. Take the production of anaphy- 

 lactic shock as an example. The theory pro- 

 posed by Wheeler and me in 1907 supposes that 

 when a given protein is first injected parenter- 

 ally into an animal, it slowly develops a specific 

 protease. This is a cellular product. Certain 

 cells stimulated by contact and by penetration 

 with the foreign protein develop a new, specific 

 protease which is capable of digesting that pro- 

 tein and no other. The protein of the first in- 

 jection is disposed of by this new specific fer- 

 ment, but is broken up so slowly that no harm 

 comes to the animal, or at least no recognizable 

 danger, from the cleavage products. The cells 

 continue in the possession of the newly acquired 

 function. This may persist for years and in- 

 deed throughout life. The animal is said to be 

 sensitized. On reinjection of the same protein 

 the body cells, having acquired the function of 

 digesting it, do so with such violence that the 

 digestive products endanger the life of the ani- 

 mal or at least develop physiological disturb- 

 ances which are easily recognizable. We have 

 offered this in explanation of the success of vac- 



