278 INFECTION AND IMMUNITY 



toneally were soon shown by Metchnikoff, 5 Bordet, 6 and others to 

 take place, though to a lesser extent, in vitro. Bordet, furthermore, 

 observed that the bacteriolytic digestive power of such immune serum, 

 when destroyed by heating, or after being attenuated by time, could 

 be restored by the addition to it of small quantities of normal blood 

 serum. It could, in other words, be "reactivated" by normal serum. 

 Prom this observation Bordet drew the conclusion that the bacteri- 

 cidal or bacteriolytic action of the serum' depended upon two distinct 

 substances. The one present in normal serum and thermolabile, he 

 conceived to be identical with Buchner's alexin. The other, more 

 stable, produced or at least increased in the serum by the process 

 of immunization, he called the "sensitizing substance." This sub- 

 stance, he believed, acting upon the bacterial cells, rendered them 

 vulnerable to the action of the alexin. Without the previous prepara- 

 tory action of the "sensitizing substance" the alexin was unable 

 to act. Without the cooperation of alexin, the ' i sensitizing sub- 

 stance" produced no visible effects. 



Bordet 's interpretation of the phenomenon of lysis differs essen- 

 tially from that of Ehrlich, in that both active serum components are 

 conceived by him, though independent, to act directly upon the 

 bacterial cell. A few years later, Bordet was able to show that 

 exactly analogous conditions governed the phenomenon known as 

 "hemolysis" or disintegration of red blood cells. 



It had been known for many years that in the transfusion of 

 blood from an animal of one species into an animal of another 

 species, injury was done to the red corpuscles which were intro- 

 duced. Observed in the test tube, the red cells in the heterologous 

 serum were seen to give up their hemoglobin in the fluid, the mix- 

 ture taking on the red transparency characteristic of what is known 

 as "laked" blood. Buchner, 7 in his alexin studies, had shown that 

 the blood-cell destroying action of the normal serum was subject 

 to the same laws as the bactericidal power of similar serum, in 

 that it was destroyed by heating, and he assumed that both the 

 bacteriolytic and the hemolytic action of normal serum were due to 

 the same "alexin." Metchnikoff, 8 moreover, had pointed out the 

 striking analogy between the two phenomena as early as 1889. 



5 Metchnikoff. Ann. de 1 'inst. Pasteur, 1895. 



9 Bordet, ibid., 1895. 



''Buchner, Arch. f. Hyg., xvii, 1893; Waremberg, Arch. d. med. exper., 1891. 



8 Metchnikoff, Ann. de 1 'inst. Pasteur, 1889. 



