830 PRECIPITINS AND THEIR APPLICATIONS 



the use of immune sera obtained from animals treated with similar materials, i.e., 

 proteins variously heated. It may be presumed that heating a complex material such 

 as animal flesh would denature some of the simple precipitinogens, and antibody ob- 

 tained through treatment with what is left unaffected would be a less complex mix- 

 ture, and the titres of simple precipitins included in such a serum would be higher than 

 were the unaltered antigen injected. These efTects, however, do not appear very clear- 

 ly, and very often more prolonged immunization with altered antigens leads to ob- 

 taining immune sera which act very much like those obtained after treatment with 

 native protein. The lability of precipitinogen, like protein in general, is such that the 

 antigen is gradually destroyed or changed as reagents continue to act upon it. 



In identification of proteins acting as precipitinogens it is obviously of great im- 

 portance to use precipitin sera giving highly specific reactions and obtained by as 

 short a course of treatment as possible. Long treatment tends to permit precipitin of 

 a minor nature to appear in response to mildly antigenic precipitinogens, and re- 

 actions deviate more and more widely from those showing the highest degree of 

 specificity obtainable. 



DIAGNOSIS 



Tests for the presence of bacterial precipitinogens as foreign protein have been 

 carried out, and through the precipitin reaction one may gain information as to the 

 nature of a bacterial species giving rise to inflammatory reactions in animal tissues. 

 It is believed that infecting organisms may liberate protein substances which diffuse 

 more or less into the body fluids, secretions, exudates, etc., and as such may be detected 

 by the use of potent precipitins. In tests such as these, non-specific reactions must be 

 especially guarded against since the fluids tested may contain a large quantity of 

 proteins produced by the infected host. These in high concentration may give false 

 positive reactions. Precipitin tests have been employed in the diagnosis of meningitis 

 by Vincent and Bellot,' and following this in many other infections. Precipitin tests 

 used in this way add to the evidence obtained by more direct means, but if considered 

 alone they would probably be of questionable value. Carrying such a procedure a 

 step farther, precipitin tests may be performed with the peritoneal fluids from mice 

 injected with pneumonic sputum and type determinations of infecting pneumococci 

 made. The results should parallel the findings with the agglutination test employed 

 for the same purpose. 



Tests with known bacterial precipitinogens have been carried out upon sera from 

 infected animals as a procedure in serum diagnosis. The infected host may have de- 

 veloped precipitins due to stimulation by the infecting micro-organisms, and the de- 

 tection of these may be of value in establishing a diagnosis. In many cases, however, 

 a suitable agglutination test will give very desirable results with less labor and fewer 

 confusing reactions. 



In a similar manner, the precipitin test has been used as an index of potency of 

 antiserum intended for therapeutic purposes. 



'Vincent, H., and Bellot: Bull, et mem. Soc. med. de hop. de Paris, 27, 952. 1909. 



