44 THE PROTEOMORPHIC THEORY AND THE NEW MEDICINE 



blood stream. The peptones of the digestive canal are believed 

 to be further hydrolized, with the production of amino-acids, 

 in their passage through the intestinal wall. The leucocyte accom- 

 plishes the same cleavage (or at all events the early parts of this 

 cleavage) in the case of foreign proteins that come to it. And 

 the quantity of these is sufficient to give full scope for the leuco- 

 cytic activities; for experiments show that the intrusion of the 

 unbroken protein molecule must be an extremely common inci- 

 dent, even if it cannot be considered a strictly normal one. More- 

 over, there are complications involved in the task of disposing 

 of these unwelcome visitors. 



The first of these complications is contingent on the fact that 

 the leucocyte is thus called upon to deal with large protein mole- 

 cules of many types, and that it can scarcely be supposed to be 

 able to do so without producing toxic cleavage molecules at some 

 stage of the process that may escape from its substance say 

 through dissolution of the body of the leucocyte itself and con- 

 taminate the blood plasma. Even though the original protein 

 was in the form of a wholesome foodstuff, say protein of beef 

 or of egg or of milk, there is always possibility that in its de- 

 compounding there may arise combinations of molecules that 

 are poisonous to the tissues of the organism. 



As Vaughan phrases it, there is a poisonous group in every 

 protein molecule. 



Possibly it would be correct to say that there are many poison 

 groups ; but Vaughan finds that their physiological effects are 

 essentially the same in all proteins. He has attempted to isolate 

 this group of molecules which, in its free state, becomes a poison 

 (so he believes) on account of the avidity with which it disrupts 

 other protein molecules. In the purest form in which he has 

 been able to isolate this group (and this is probably, he conceives, 

 far from chemical purity), it kills guinea pigs of from two hun- 

 dred to three hundred grams weight, when injected intracar- 

 diacally in doses of half a milligram. In the original protein 

 molecule, it is held, the poisonous group is physiologically inert, 

 because it is combined with secondary groups called side-chains. 

 But these secondary groups are detached or decompounded in the 

 proteolysis of the molecule ; and there is conceivable danger that 

 during this process the poisonous group may become detached 

 and, diffusing in the blood stream, exert a toxic effect on the 

 central nervous system. There are no observed phenomena asso- 

 ciated with the therapeutic parenteral introduction of the pro- 

 teins that suggest this, however, unless the anaphylactic reaction 

 occasionally induced be so interpreted. 



The danger of such a result when proteins are digested in the 

 alimentary tract is small, because the poisonous group is prob- 



