THE PHENOMENON OF PRECIPITATION 259 



It is immediately evident that these investigations are closely 

 analogous to those of Joos and others on the agglutinins. The anti- 

 serum produced with the heated antigen here again reacts both with 

 the native and with the heated antigen, whereas the antiserum pro- 

 duced with the native unheated antigen reacts only with the un- 

 heated. The "heat-precipitins" therefore may be also called "um- 

 fanglicher" the term applied by Paltauf to the agglutinins pro- 

 duced with heated bacteria. 



Schmidt, 36 who has studied the problem extensively, finds that 

 heating serum protein to 70 C. for as long as 30 to 60 minutes 

 alters its precipitability by "native precipitin" (precipitin produced 

 by immunization with native unheated serum) only in so far as it 

 diminishes the delicacy of the reaction by 10 to 30 per cent., and 

 that heating to 90 C. for as long as an hour does not render it en- 

 tirely non-precipitable, so that protein so treated may yet be detect- 

 able by ordinary specific precipitins produced by injections of un- 

 heated serum, though the delicacy of the reaction is lessened. Boil- 

 ing, according to Schmidt, renders the antigen no longer precipitable 

 by such "native precipitin," but, on the other hand, it does not seem 

 to destroy its antigenic property of inciting precipitins on injection 

 into animals. Fornet and Miiller, on the other hand, claim that even 

 boiled protein can be detected by "native precipitins," though the 

 reaction is only about one-tenth as delicate as it is with unheated 

 protein. 



Schmidt studied these relations especially as they affect the per- 

 formance of specific precipitin reactions in the identification of 

 boiled meat. He found that when he immunized rabbits with serum 

 protein that had been heated at 70 C. for 30 minutes the antiserum 

 so obtained gave strong and practically useful reactions with its 

 specific antigen even if this had been boiled. Since "native pre- 

 cipitin" gives weak reactions only with such a boiled protein, 

 Schmidt recommends the use of the "TO precipitin" (produced by 

 injections of heated serum) for tests in which a heated antigen is to 

 be identified. 



He states, however, that very prolonged heating may so com- 

 pletely coagulate the antigen that none of it can be gotten into "solu- 

 tion" (suspension), and in such cases results can be obtained neither 

 with the "native" nor with the "70 precipitin." He has at- 

 tempted, therefore, to find a method whereby even such entirely 

 insoluble proteins may be identified, and claims to have succeeded 

 by preparing what he calls his "heat-alkali-precipitin." 37 He di- 



36 Schmidt. Biochem. ZeitscJir., 14, 1908; also Zeitschr. f. Imm., Vol. 

 13, 1912. 



37 "Native precipitin" = precipitin produced by injections of normal un- 

 heated serum. 



"70 precipitin" = precipitiif produced by injections of serum heated 

 to 70 C. for 30 minutes. 



