STUDIES ON CYTOLYSINS 67 



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reaction with a serum sensitized to egg albumin upon mixing it 

 with egg albumin diluted 1,000,000 times. The delicacy of such 

 tests can be appreciated when one knows that ordinary chemi- 

 cal tests cease to give reactions in blood diluted 1000 times. 



As long ago as 1895 Bordet found that the blood of guinea- 

 pigs which had been repeatedly injected with the red corpuscles 

 of the rabbit acquired peculiar properties. Serum prepared 

 from these sensitized guinea-pigs, when placed in a test-tube 

 with rabbits' blood, not only caused the agglutination of the 

 red blood corpuscles, but even rapidly dissolved them. The 

 serum of untreated guinea-pigs was incapable of doing this or 

 did it only feebly. Bordet showed further that this enhanced 

 solvent action of the serum of animals treated with rabbit cor- 

 puscles existed only for the red cells of the rabbit, not for those 

 of other species of animals. Exceptions to this rule have since 

 been found, though in the main the action is a specific one. 

 The action is known as hemolysis, and the substance in the 

 serum which brings about solution of the red cells is termed a 

 hemolysin. 



Hemolysins are now known to be special members of a gen- 

 eral class of substances termed cytotoxins or cytolysins. For 

 just as alien red blood cells lead to the production of hemolysins, 

 so various other materials, as leucocytes, nervous tissue, sper- 

 matozoa, and crystalline lens, when injected into the blood of an 

 unrelated species, will form lytic substances more or less specific 

 for the antigen used in the sensitizing process. All the cyto- 

 lytic sera so far studied have been found to be more or less 

 hemolytic, and it is probable that none acts exclusively upon 

 its own antigen. The important fact, for our purposes, is that 

 although a particular cytolytic serum may affect some other 

 tissues, it vigorously attacks the special tissue used as antigen. 

 The exact nature of antibodies, such as precipitins, cytoly- 

 sins and others, or the manner in which they are engendered is 

 not known. The blood is probably in the main the carrier rather 

 than the producer of such bodies. While the leucocytes may be 

 one source of certain constituents, it is probable that various 

 tissues of the body are responsible. There is evidence to show 



