230 ILEMOLYSINS 



sensitized organisms and remains in the serum. Its action is like that of a 

 dye which only dyes a fabric that has been treated with a mordant. 



To sum up : in the serum of immunized animals a specific substance, 

 the immune body, is present which unites on the one hand with its 

 corresponding micro-organism and on the other hand with a substance, 

 alexin or complement, pre-existing in the serum of all normal animals. 

 Upon this interaction of two bodies, in which the immune body plays a 

 part similar to that of a mordant in dyeing, depends the destruction of 

 the micro-organisms in Pfeiffer's experiment. 



The interaction of complement with the micro-organism through the immune 

 body is diagrammatically represented in the figure (fig. 159). 



Note. It is important to observe that the phenomena just studied are not 

 seen in the case of all micro-organisms. The combined action of the immune 

 body and complement only leads to destruction in the case of very delicate 

 organisms, e.g. the cholera vibrio and the typhoid bacillus. 



In the majority of cases the pathogenic micro-organisms are much more 

 resistant to the bactericidal action of the immune serums and no bactericidal 

 action can be seen ; but though not visible, combination of the immune body 

 with the complement nevertheless takes place, and the organisms are rendered 

 more easy of destruction by the leucocytes (vide opsonins). 



In studying the phenomena of complement fixation (vide infra) it will be 

 shown how the action of the immune body on the more resistant organisms 

 may be demonstrated. 



Haemolysins. 



Haemolysis means the destruction of the red cells of the blood with diffusion 

 of the haemoglobin into the medium in which they are suspended. 



If a quantity of red cells be suspended in an hypotonic solution, distilled 

 water for example, they undergo haemolysis. On the other hand, in an 

 isotonic fluid, normal saline solution for instance, the red cells may remain 

 intact for a very long time. Similarly in the serum of the majority of normal 

 animals the red cells undergo no alteration. To this general rule, however, 

 there are a few exceptions ; dogs' serum, for instance, hsemolyzes guinea-pig 

 red cells ; eel serum hsemolyzes all mammalian red cells, and so on. 



The inoculation of large doses of red cells of one species of animal into the 

 peritoneal cavity of another species produces a toxic effect and may kill the 

 animal inoculated. 



On the other hand, if small quantities be inoculated on several successive 

 occasions there is a minimal reaction and death does not take place. In 

 the latter case the serum of the inoculated animal is capable of destroying 

 the red cells of the animal species used for inoculation in vitro and is there- 

 fore said to exhibit haemolytic properties (Bordet). 



For example, if a guinea-pig be inoculated with rabbit red cells, the guinea- 

 pig's serum will become haemolytic for rabbit red cells. 



Preparation of an haemolytic serum. Under no conditions must the whole 

 blood be inoculated but only the washed red cells. 



1. Collect some blood under aseptic precautions, and after defibrinating it 

 (p. 36) centrifuge. Thus, into each tube of the centrifuge pour equal parts 

 of defibrinated blood and sterile normal saline solution, centrifuge, and when 

 the red cells are all precipitated at the bottom of the tube pipette off the 

 clear supernatant liquid with a bulb pipette. Fill up the tube with fresh 

 saline solution, stir up the deposit and centrifuge again. Repeat the opera- 

 tion three times. 



