THE LEUCOCYTES IN IMMUNITY. 737 



appears in very great quantity as a result of these injections. 

 M. de Dugern 71 has confirmed this observation,, and has added 

 the interesting fact that the sensitizing substance is found in 

 great excess in the serum of prepared animals. When fresh, 

 non-heated blood is added to this serum, the haemolysis produced 

 is thirty times more active than occurs with the serum of the 

 prepared animal alone." How could haemolysis be increased 

 thirty times simply by adding" the sensitizing substance, our 

 oxidizing substance, "which," using MetchnikofFs words, 

 "fixes itself to the red corpuscle without ever dissolving it," 

 a feature which, he adds, "is accepted by everyone and may be 

 regarded as definitely settled"? In the light of our statements 

 regarding fibrinogen, this body cannot be considered as the 

 haBmolytic agent, since the blood-cells remained intact when 

 in the first experiment they had been set free by the addition 

 of fresh serum. In the latter experiment, however, the pres- 

 ence of alexin, the trypsin-containing body, is alluded to, even 

 though supposed to be present only in normal quantities. This 

 suggests that this trypsin may have played a role in the process 

 not only in this, but likewise in the former experiment. 



This is further sustained by the need of an agglutinating 

 agent, for we have seen that, although heating caused the serum 

 of an injected animal to lose its corpuscle-destroying character, 

 its agglutinating power remained. We know the peculiar man- 

 ner in which trypsin attacks albuminoids; it does not disin- 

 tegrate them as do some other bodies by abstracting one or 

 more of their constituents; it fairly corrodes the substances 

 vulnerable to it, first melting corners, edges, etc., and softening 

 the surface until the entire fragment has disappeared as would 

 a gum-drop in water. Agglutination seems a normal outcome 

 of such changes. Under these circumstances, however, trypsin 

 cannot, as an agglutinant, be considered as a part of the alexin 

 destroyed by heating to 55 C. or thereabouts, and must have, 

 in the foregoing experiments, been liberated from the alexin 

 by the heating process, thus being free to act when fibrinogen 

 and oxidizing substance were present. In other words, it must 

 also have been able to stand without harm the higher tempera- 



71 M. de Dugern: Miinchener med. Wochenschrift, No. 20, p. 677, 1900. 



