AGGLUTININS AND PRECIPITINS 113 



until it is possible to isolate the protein of other body organs without 

 contamination by the animal's blood. Up to the present time this 

 seems to be impossible. Studies by Bell, for example, with perfusion 

 of various organs has demonstrated the impossibility of removing the 

 blood completely. 



Detection of Food Adulteration. The precipitin reaction is ap- 

 plied not only to detect blood as indicated above but also various other 

 body proteins; for example, it may be used to detect the nature of 

 bone fragments or other tissue scraps. Of great significance is the 

 fact that the precipitin test is employed for the detection of adultera- 

 tion of food products. It has been utilized, for example, in detecting 

 adulteration of sausages by the use of horse and other meats. In the 

 preparation of such food products, heat is often employed, and there- 

 fore it is necessary to know the influence of heat on the precipitin 

 reaction. The relation of heat to the agglutinin reaction has already 

 been discussed (see page 93), and it is found that similar conditions 

 exist in regard to the precipitin test. Obermeier and Pick studied this 

 problem experimentally and found that an anti serum, even of high titer, 

 produced by an unheated antigen, failed to precipitate when brought 

 into contact with heated serum. If, however, animals are immunized 

 with serum boiled for a short time, the resulting immune serum forms 

 a precipitate when brought in contact with either heated serum or 

 unheated serum. Therefore, the precipitin produced by the latter 

 method is regarded as more comprehensive in its precipitating activity, 

 but nevertheless its species specificity remains unimpaired. By em- 

 ploying a lower degree of heat, namely 70 C., Schmidt found that 

 this marked difference was not so apparent and that an immune serum 

 prepared by injecting unheated serum would produce precipitation 

 with unheated serum and with the moderately-heated serum. How- 

 ever, the titer of antiserum prepared by the use of moderately-heated 

 antigen was not as high as with the use of unheated antigen. Schmidt 

 ifurther found that he could produce an even more comprehensive 

 immune serum by boiling the antigen until a coagulum was formed, 

 namely, for three hours. The coagulum was washed with salt solution, 

 dried, powdered and then taken up with a normal NaOH solution. 

 Zinsser and Ottenberg found that the use of a boiled antigen led to 

 the production of a comprehensive precipitin, but nevertheless they 

 determined that this resulted in some loss of specificity of the precipitin. 



This outline of the influence of heat will serve to show that in the 

 detection of the adulteration of food products extreme care must be 

 taken in the selection of material. Wherever possible, fresh material 

 should be obtained, and the material for testing should always be taken 

 from near the middle of the specimen. This precaution prevents con- 

 tamination with other meat, and in the case of sausage yields material 

 likely to be less influenced by heat or smoke. The meat is cut into fine 

 pieces and allowed to extract in salt solution. Clarke used 30 grams 

 meat and 50 c.c. physiological saline, extracting in the ice chest for 

 twenty-four hours, and further diluting 1-300 for the test. Such 

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