182 INFECTION AND RESISTANCE 



which prevents its functionation in the simultaneous presence of 

 end-piece, but does not seem to interfere with its ability to combine 

 with the sensitized cells. As was to be expected, explanation for 

 this has been sought by the Ehrlich school in changes of affinity. 

 Sachs suggests that the mid-piece, by its preservation in salt solution, 

 has lost its avidity for the sensitized cells and has gained in avidity 

 for the end-piece, an alteration which therefore prevents its union 

 with the cells. The same idea was suggested by Hecker himself. It is 

 a little difficult to reconcile this explanation, however, with the fact 

 that whole serum can be preserved and remain active in its comple- 

 mentary function for a number of days, mid-piece and end-piece 

 being present together, in a medium which, as far as salt contents are 

 concerned, is isotonic with the salt solution in which mid-piece de- 

 teriorates so rapidly w r hen alone. 



That there is, after all, much similarity between the alexins of 

 different animals is evident from the fact that, as Marks and others 

 have shown, the end-piece of one animal may activate the mid-piece 

 of another species. It appears also from experiments like those of 

 Ritz and Sachs 5T that an animal may possess a mid-piece for certain 

 sensitized cell complexes without possessing a corresponding end- 

 piece. Thus they found that the serum of mice contained a mid- 

 piece but not an end-piece for sensitized guinea pig corpuscles. 



Much that has been found out about the so-called globulin portion, 

 moreover, tends to engender doubt as to the wisdom of applying to 

 these complement fractions the terms "mid-piece" and "end-piece," 

 an objection which is based upon reasons similar to those which pre- 

 vent Bordet from accepting the term amboceptor. For so little is 

 actually known concerning the mechanism of complement functiona- 

 tion, that it seems unwise to establish on a firm basis a preconceived 

 idea of the mechanism by adapting the terminology to a theory. The 

 most confusing feature of the problem lies in the surprising quantita- 

 tive relations which seem to exist in the reactions of the two frac- 

 tions. Thus Liefmann and Cohn 58 claim that in the presence of 

 moderately sensitized cells no measurable amount of the so-called 

 mid-piece or globulin fraction is bound, that is, removed from solu- 

 tion ; and yet, when both fractions are added to such cells, rapid and 

 complete hemolysis results. In the presence of heavily sensitized 

 cells (20 to 50 units) a small quantity only is removed. Nevertheless 

 this fraction has had a demonstrable effect on the cells, since it has 

 rendered them amenable to the action of the albumin fraction. In all 

 such experiments, therefore, as Liefmann justly points out, the de- 

 gree of sensitization must be taken into consideration before conclu- 

 sions are formulated. It is curious also that a slight excess of the 

 globulin fraction may prevent complement action completely. In 



57 Ritz and Sachs. Zeitschr. f. Imm., Vol. 14, 1912. 



58 Liefmann and Cohn. Zeitschr. f. Imm., Vol. 7, 1910. 



