57 



unite with c in order to acquire the energy for union with b. 

 Pick's suggestion is that, in antigen-antibody reactions, the 

 colloidal reaction is intermediary and provides the energy 

 necessary for the subsequent reaction which involves changes 

 in chemical structure. 



This view, it will be observed, demands some expansion of 

 ideas about specific reactions in the animal body. In some cases, 

 a simple explanation may suffice. The reaction may commence 

 with a specific union between antibody and bacterial antigen; 

 and then the bodily mechanism may step in and complete the 

 antibacterial process in a non-specific manner. But, in other 

 cases, the process may be much more complicated, and it may 

 be impossible to draw a hard-and-fast line between a specific 

 and a non-specific part of the reaction. For example, the 

 antibody, in the form of an immune serum used for conferring 

 passive immunity, may react first with some constituent of the 

 animal body, as a preliminary to acquirement of energy for 

 specific action on the bacterial antigen; i.e., the specificity of 

 the reaction may be due to the combined, influences of antibody 

 and the animal's natural mechanism of resistance, not to the 

 former alone. 



5. Chemico-Physical Equilibrium in Relation to the Conception 

 of Antibodies. — " Physiological equilibrium " and " the disturb- 

 ance of this equilibrium in disease " are phrases which are readily 

 understood; but the relation of "equilibrium" to antibodies 

 requires some explanation. Perhaps this subject may be intro- 

 duced by describing it as an attempt to give more accurate 

 scientific expression to what, according to the Ehrlich school, 

 would be termed a " habit." I refer to the familiar doctrine 

 that the reason why an animal keeps on turning out amboceptor, 

 long after the antigen which provided the original stimulus has 

 disappeared, is that the animal's cells have acquired the " habit " 

 of doing so. If the animal's mechanism were simply a com- 

 plicated problem in mechanics, one might substitute " resultant " 

 for " habit " ; i.e., the normal play of interacting forces has a 

 particular resultant force a as its outcome ; but these interacting 

 forces are so numerous and complicated that the slight jar 

 caused by a new force 6 (the antigen) dislocates the whole 

 mechanism ; hence it is not a case of finding the resultant between 

 a and 6 ; the new resultant c is mainly due to a rearrangement 

 of all the forces which previously gave resultant a ; and, therefore, 

 c may persist after the relatively insignificant force 6 has dis- 

 appeared. But, of course, " resultant," as the term is used in 

 elementary physics, is not adequate to explain vital phenomena. 



Vital processes may be regarded, in one aspect, as interactions 

 between the innumerable colloidal constituents of the humoral 

 and cellular elements of the body. These interactions, at any 

 given time, tend to find an equilibrium which is determined by 

 the quantitative as well as by the qualitative conditions of the 

 interacting substances, and represent the potential properties 



