io8 Immunity 



ferent blood-serums possessed the power of killing bacteria in 

 large numbers, but that the bactericidal power of the serum soon 

 disappeared, after which the serum became a good culture-medium 

 for the very bacteria it had formerly destroyed. Metschnikoff 

 objected to the observations, declaring that all the phenomena were 

 ultimately referable to the leukocytes, so Nuttall investigated peri- 

 cardial fluid and the aqueous humor of the eye, which were also 

 found to possess bactericidal powers. 



The matter was next taken up by Buchner and his associates,* 

 who showed that the blood-plasma and blood-serum possessed 

 exactly the same bactericidal effects as the total blood. Buchner 

 and Nuttall both showed that the exposure of the bactericidal fluids 

 to a temperature of 56C. for a few hours entirely destroyed their 

 activity, though low temperatures were without effect upon them. 

 Buchner found that the exposure of the serum to sunlight and oxygen 

 also destroyed the bactericidal power. Neutralization of alkaline 

 serum did not destroy its activity, but when the serum was dialyzed 

 and the NaCl removed from it, the germicidal power was lost, to 

 return again when it was restored. Buchner called the bactericidal 

 principle alexin. 



Many interesting facts were collected bearing upon the bactericidal 

 substance or alexin. Thus Morof showed that it was proportionally 

 more active in sucking infants than in adults, and Ehrlich and 

 Brieger J found that it passed from mother to offspring in the milk. 



At first Buchner regarded alexin as an albumin, but later he 

 came to look upon it as a proteolytic enzyme, this view no doubt 

 resulting from an endeavor to explain the relation of alexin to im- 

 munity against intoxication, in which it was necessary to show that 

 alexin not only killed bacteria, but also destroyed toxins. 



Hankin|| endeavored to show that there were differences between 

 the substances destroying the bacteria and those acting upon their 

 toxic products. To the whole group he applied the term defensive 

 proteins. Those present in natural immunity he called sozins. 

 those found in acquired immunity phylaxins. Sozins with bacteri- 

 cidal activity he further described as mycosozins, those with toxin- 

 destroying activities as toxosozins. Phylaxins with bactericidal 

 action were called my co phylaxins; those with toxin-destroying 

 properties toxo phylaxins. 



Metschnikoff found it unnecessary to modify his ideas, but per- 

 sisted in referring all the phenomena to the phagocytes or to enzymes 

 derived from them. 



At this point it will be evident to the reader that the phagocytic 



*"Centralbl. f. Bakt.," etc., 1889, Bd. v, 817; vi, i; "Archiv fur Hygiene," 

 1891, x, S. 727; "Centralbl. f. Bakt.," etc., 1890, vn, 76. 

 f " Jahresb. f. Kinderheilkunde," v, 396. 

 j "Zeitschrift fur Hyg.," 1893, xni, 336. 

 "Munch, med. Woch.," 1899. 

 If "Centralbl. f. Bakt.," etc., xn, Nos. 22, 23; xiv, No. 25. 



