THE PHENOMENON OF PRECIPITATION 271 



lead to a sudden elimination of the colloidal protective action, union 

 of the antigen and antibody, and, by the mechanism just outlined, 

 a naphy lactic shock. 



The fact, moreover, that mere heating will change the precipi- 

 tating action, which certain sera have on inorganic colloids, to a 

 protective one seems to show that this latter function may justly 

 be associated with delicate physical or chemical alterations of animal 

 sera. 



Furthermore, this point of view is strengthened by the fact that 

 the mutual precipitation of sera, such as those described, takes place 

 slowly, as does the mutual precipitation of two protected colloidal 

 mixtures, in contradistinction to the more rapid precipitation which 

 takes place when any of these sera is added to an antigen dilution, 

 where the element of protection may be assumed to be practically 

 eliminated by more extensively changed quantitative relations. 



This point of view has lately been disputed by Weil, who has gone 

 back to the older view of von Dungern, largely on the basis of pre- 

 cipitation experiments he carried out with crystallized egg albumen. 

 Weil claims that if a pure protein, like crystallized egg albumen, is 

 used for immunization, antigen and antibody are never found simul- 

 taneously in the blood stream. If this were true it would indeed con- 

 stitute a very important contradiction of our point of view. In con- 

 sequence Bayne-Jones carried out similar experiments in our labora- 

 tory, and found that even with the purest obtainable recrystallized 

 egg albumen both antigen and antibody are at times demonstrable 

 in the blood. He showed this both by precipitation and by comple- 

 ment fixation. We do not consider the question closed, however, be- 

 cause it is indeed true that when working with a purified protein it 

 is more difficult to demonstrate the two substances in any quantity, 

 than it is when the crude serum antigen- is used. This may be, of 

 course, due to the fact that pure egg albumen may be more rapidly 

 assimilated and remains in the circulation for a less extensive period 

 than does the crude antigen. However, further experiments in this 

 direction will unquestionably clear the matter up because it is a 

 simple question of fact amenable to experiment. 



As far as the separation of a pure albumen from an albumen 

 globulin mixture is concerned, we feel rather doubtful whether such 

 a sharp separation can be made and are inclined to lean towards the 

 view expressed by Wells some years ago, that the various proteins 

 (that is, albumens and globulins) of the same animal material are not 

 sharply separable but shade one into the next as in a spectrum. This 

 view is the more likely when we consider that our methods of separa- 

 ting these various proteins are purely physical methods of heating 

 and of precipitation by salts. 



