1 68 BACTERIOLOGICAL METHODS 



water bath until the muscle fibers are disintegrated. Boil down to 

 50 grams and filter. When cool add an equal part of dilute nitric 

 acid (10 per cent.) to precipitate the albuminoids, and again filter. 

 Pour the filtrate into a test-tube and carefully pour iodine water 

 down the inside of the tube. If horse meat is present a burgundy 

 red zone appears at the point of contact of the two solutions. The 

 width and intensity of the colored zone is in direct proportion to the 

 amount of horse meat present. 



If starch is present (as in sausages and sausage meats seasoned 

 with starch -bearing spices or mixed with starch fillers), this must be 

 precipitated from the boiled meat extract and removed by filtra- 

 tion. To the extract add two or three times the volume of con- 

 centrated acetic acid and let stand for 2 or 3 hr., and then 

 filter through two or three thicknesses of filter paper. Test 

 the filtrate with the iodine water as above suggested. However, 

 before making the glycogen test the test for starch should be 

 appHed, for if it responds to this test the precipitation of starch 

 must be repeated. Because of the dilution with the three or more 

 volumes of acetic acid (to precipitate the starch) negative re- 

 sults may be obtained in cases where horse meat is present. It 

 is therefore advisable to precipitate the glycogen by means of 

 alcohol, using from teii to twelve times the volume of the acidu- 

 lated meat filtrate. The cloudy alcoholic suspension is run 

 through a small filter and the precipitated glycogen on and in 

 the filter paper is washed out by means of hot acidulated (acetic 

 acid) water, and this filtrate is then tested with the iodine water. 

 This test is positive in the presence of 5 per cent, quantities of 

 horse meat. The wine-red color reaction is temporary only and 

 it must be kept in mind that dextrin interferes with the reaction. 



Because of the fact that meats other than that derived from 

 the horse may contain glycogen, it is sometimes necessary to 

 supplement the above color reaction with the biological test or 

 the precipitin test which has come into use within recent years. 

 The general routine for making the test is as follows: Inject 



