150 ANTIGENS AND THE TECHNIC OF SERUM REACTIONS 



group is very labile and readily becomes non-functionating, but the 

 combining group is relatively stabile. A precipitin which has lost 

 its ergophore group is called a precipitinoid. 



The precipitate formed by a specific serum acting upon a clear 

 solution of the antigen (precipitinogen) probably is derived from the 

 serum, because very dilute solutions of the immunizing protein will 

 throw down a relatively bulky precipitate, far too great in amount 

 to come from the antigen in the dilution used. 1 



Precipitins have been extensively studied in their relation to cer- 

 tain aspects of Forensic Medicine, but they have little practical value 

 in the laboratory diagnosis of bacterial disease. They are found in 

 sera under the same conditions as agglutinins, but the technic for their 

 demonstration is more involved than that for agglutinins. Their 

 relation to immunity is unknown, but probably similar to that of 

 agglutinins. 



LYSINS. 



Mention has been made (see preceding section) of the bactericidal 

 power of fresh blood serum of a normal animal and man. This impor- 

 tant discovery, that normal sera contain substances that will destroy 

 moderate numbers of bacteria, was made by Nuttall, 2 who also 

 observed that there was a limit to this destructive activity and that 

 this property was lost upon standing, or rapidly destroyed by an 

 exposure of the serum to 55 C. for half an hour. Buchner 3 corrobo- 

 rated and extended these observations and designated the unknown 

 stabile component "alexin." Pfeiffer 4 then showed that the destruc- 

 tive action of normal sera could be increased many fold above its 

 original level for a specific organism if that organism were repeatedly 

 injected into an animal in sublethal, but gradually increased doses. 

 The serum of such an animal'would still destroy only moderate num- 

 bers of heterologous bacteria, but relatively great numbers of the 

 homologous bacteria . This observation opened the way for the highly 

 important study of active acquired immunity against bacteria. 

 Pfeiffer observed that heating immune sera to 50 to 56 C. for half 

 an hour destroyed their bactericidal properties, precisely as Nuttall 

 had found that natural, non-specific bactericidal properties were 

 destroyed under similar conditions. Bordet 5 then discovered that the 



1 Welsh and Chapman, Ztschr. f. Immunitasforsch., 1911, ix, 517. 



2 Ztschr. f. Hyg., 1888, iv, 353. 



3 Cent. f. Bakt., 1889, v, 817; vi, 1, 561. 



4 Ztschr. f. Hyg., 1894, xviii, 1; 1895, xix, 75-100. 

 6 Ann. Inst. Past., 1895. 



