128 Immunity 



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 observa- 

 tions, declaring that all the phenomena were ultimately 

 referable to the leukocytes, so Nuttall investigated pen- 

 cardial fluid arid the aqueous humor of the eye, which were 

 also found to possess bactericidal powers. 



The matter was next taken up by Buchner and his as- 

 sociates,* 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 56 C. 

 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. Neutraliza- 

 tion 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 BriegerJ 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 immunity 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 act- 

 ing upon their toxic products. To the whole group he applied 

 the term defensive proteids. Those present in natural im- 

 munity he called sozins, those found in acquired. immunity 

 phylaxins. Sozins with bactericidal activity he further de- 



* " Centralbl. f Bakt .," etc , 1889, Bd v,S. 817; vi, S. 1; "Archivfur 

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

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

 t "Zeitschrift fur Hyg.," 1893, xm, S. 336. 

 "Munch, med. Woch.." 1899 

 II "Centralbl. f. Bakt.," etc., xn, Nos. 22, 23: xiv. No. 25. 



