ii6 THE PRINCIPLES OF IMMUNOLOGY 



Introduction. In the study of resistance to disease it was learned 

 very early in the course of the investigations that the blood serum 

 possesses the property of destroying bacteria. Later it was found that 

 blood serum may possess similar power in regard to other cells, in- 

 cluding various animal cells, particularly the erythrocytes. Rather 

 than consider the subject of cytolysis in a historical fashion, we believe 

 that it may be much more clearly discussed by first presenting the 

 established facts which have been learned concerning the power of 

 blood serum to destroy red blood-corpuscles. Many substances other 

 than blood serum may destroy erythrocytes and immunology has 

 profited from the study of hemolysis resulting from chemical and 

 physical agents, but the greatest advance has been made by the investi- 

 gation of the hemolytic properties of the blood. 



Hemolysins. Hemolysins are classified, in the same manner as 

 hemagglutinins, into autohemolysins, iso-hemolysins and hetero- 

 hemolysins. These may be present normally or may be produced as a 

 result of immunization. Landois in 1875 studied those normal hetero- 

 hemolysins which for years have made blood transfusion a dangerous 

 operation and showed that fresh sera from various species possess the 

 power of dissolving or laking the erythrocytes of certain foreign species. 

 In 1898 Belfanti and Carbone noticed that the serum of a horse which 

 had received numerous injections of rabbit blood was, upon injection, 

 specifically toxic for rabbits, but they did not determine the cause of 

 the toxicity. In the same year Bordet published his discovery of the 

 fact that several injections of defibrinated rabbit blood into the peri- 

 toneal cavity of guinea-pigs led to the production of an immune body in 

 the guinea-pig serum capable of rapidly laking rabbit erythrocytes, 

 whereas normal guinea-pig serum possesses the same property in only 

 slight degree or not at all. Shortly afterward von Dungern and Land- 

 steiner independently published similar results. The immune body 

 in the serum has been named hemolysin and also hemotoxin, but the 

 former term has received much wider usage, because the constitution 

 of this body is not that of true toxins, because the effect is seen on the 

 blood-corpuscles rather than the whole blood, and because the hemo- 

 globin is liberated for solution in the surrounding medium without 

 actual destruction of the stroma. Bordet in his study of the subject 

 showed that heating the serum to 55 C. for thirty minutes so altered 

 it that it no longer produced hemolysis; in other words, it became 

 " inactive." It could, however, be reactivated by the addition of a 

 small amount of fresh normal serum. This indicated that two sub- 

 stances are concerned in the hemolytic activity of blood serum, a 

 thermostable substance present in the immune blood and a thermolabile 

 substance present in normal blood as well as in immune blood. Bordet 

 named the immune thermostable body " substance sensibilisatrice " and 

 Buchner named the thermolabile body " alexine." Ehrlich and Morgen- 

 roth, whose studies have been of fundamental importance, named the 

 thermostable body " amboceptor " and the thermolabile body " com- 

 plement." Others have given other names, but these two forms of 



