THE PHENOMENON OF PRECIPITATION 261 



cipitable, and no longer produces precipitin when injected into 

 animals. 



The striking feature of these experiments is that they show a 

 gradual alteration of the protein first by heat, then by alkali and 

 heat, in such a way that the antigenic properties are changed but 

 not destroyed. Each precipitin, moreover, seems to react most 

 strongly with the particular antigen-alteration which produced it, 

 and, according to Schmidt, retains its species specificity. This is 

 not the case with the iodized proteins and nitroproteins and diazo- 

 proteins produced by Obermeyer and Pick. 38 Here iodized beef 

 protein injected into animals produced a precipitin which reacted 

 with the iodized protein, not only of the beef, but also similarly 

 altered proteins of other animals and the same was true of the 

 nitro and diazo modifications. 



Although the experiments of Schmidt have great theoretical 

 value, their practical utilization must depend upon the degree of 

 specificity possessed by the heat-precipitins or the heat-alkali-pre- 

 cipitins. In Obermeyer and Pick's original investigations we have 

 seen that they found the precipitin produced with heated serum as 

 strictly specific as that induced by native serum. This has also been 

 the experience of Schmidt. Fornet and Miiller, 39 on the other hand, 

 report that the precipitins produced by them with heated muscle- 

 protein were not as strictly specific as those produced with the un- 

 heated in that the former gave precipitates, not only with homol- 

 ogous protein solutions, but with foreign proteins in moderate con- 

 centration as well. In experiments carried out by the writer with 

 Ostenberg 40 it was attempted to determine whether or not precipi- 

 tins could be produced by injecting animals with protein that had 

 been boiled, and if so what the action of these substances would be 

 upon boiled proteins. Contrary to the results of Fornet and Miiller, 

 it was actually found that sera boiled for 3 to 5 minutes injected into 

 rabbits induced precipitins which acted upon boiled proteins, but at 

 the same time it was determined that the antibodies so produced 

 were no longer strictly specific. The protocol given at the top of the 

 next page will illustiate these experiments. 



Summarizing these results together with those of Fornet and 

 Miiller and of Schmidt it would seem that the injection of boiled 

 proteins induces precipitins which no longer act on native antigen, 

 which act powerfully on boiled antigen, but are no longer strictly 

 specific. This seems ta us of great theoretical interest as showing 

 an alteration by heating in the species adherence of the antigen. 

 Practically, therefore, precipitins produced with boiled protein are 

 of little value, and forensic determinations of boiled proteins should 



38 Obermeyer and Pick. Wien. klin. Woch., No. 12, 1906. 



39 Fornet and Miiller. Zeitschr. f. Hyg., Vol. 66, 1910. 



40 Zinsser and Ostenberg. Proc. N. Y. Pathol. Soc., 1914. 



