444 Dr. Paul Ehrlich. 



affinity for a corresponding haptophore group of the red blood corpuscles, 

 and with which at lower temperatures it quickly unites, and another 

 haptophore group of a lesser chemical affinity, which at a higher tem- 

 perature becomes united with the "complement" present in the 

 serum. Therefore, at the higher temperature, the red blood corpuscles 

 will draw to themselves those molecules of the " immune body " which 

 in the fluid have previously become united with the " complement." 

 In this case the " immune body " represents in a measure the connect- 

 ing chain which binds the complement to the red blood corpuscles, and 

 so brings them under its deleterious influence. Since under the 

 influence of the " complement " — at least, in the case of the bacteria — 

 appearances are to be observed (for example, in the Pfeifl'er phe- 

 nomenon) which must be regarded as analogous to digestion, we shall 

 not seriously err if we ascribe to this " complement " a ferment-like 

 character. 



It is obvious that when the normal serum of one animal possesses 

 haemolytic action on the blood of another, the component of the haemo- 

 lysine which here unites with the red blood corpuscle and forms the 

 connecting link between it and the " complement " which is essential 

 to the occurrence of solution, cannot, in the absence of any preceding 

 process of immunisation, be designated "immune body." In its 

 characteristics and action, however, it only difl'ers from this in occur- 

 ring naturally, and may well be designated " intermediate body " 

 (Zwischenkorper). It may here be stated that the constitution of a 

 hsemolysine is graphically represented in fig. 7, Plate 7. 



Yery important for the conclusion that only with the assistance of the 

 "intermediate body" or of the "immune body" can the "comple- 

 ment," which leads to the solution, become united with the blood 

 corpuscle, is the following experiment. The serum of the dog has very 

 considerable solvent action upon guinea-pig's blood, but loses this pro- 

 perty if warmed. If dog's serum, thus rendered inactive by warming, 

 is brought into contact with suspended corpuscles of guinea-pig's blood, 

 these are not dissolved ; but, if to such a mixture there be also added 

 guinea-pig serum, i.e., the serum normal to these red blood corpuscles, 

 the erythrocytes are at once dissolved. Here the only explanation 

 is that the "intermediate body," which possesses a specific affinity 

 for guinea-pig erythrocytes, and is present in the inactive dog's serum, 

 is able to seize on one of the many " complements " present in guinea- 

 pig's serum, with the result that the " complement " which cannot 

 normally attach itself to the corpuscles, comes now to exercise its 

 destructive influence. 



We see at the same time from this experiment that the haemolysines 

 occurring naturally, obey the same laws as those produced through the 

 process of immunising. In fact, for them also, in a great number of 

 instances, precisely similar behaviour has been demonstrated. 



