TRANSMISSION OF TOXINS THROUGH MILK 245 



repeated every four or five days for three weeks or at close inter- 

 vals. The blood-serum of this rabbit will then produce a pre- 

 cipitate with highly diluted milk of the same species, but no 

 precipitate with other kinds of milk. However, there are two 

 complicating factors in this test, namely: 1, the milk must be 

 diluted highly enough to be fairly clear, otherwise a shght pre- 

 cipitate cannot be observed; and 2, when milk is highly diluted 

 relatively small amounts of the adulterant escape detection. 

 Furthermore, it should be remembered that the precipitin reaction 

 is not strictly specific and a precipitate will be formed with milk 

 from mammals closely related to each other. 



The precipitin test is carried out by placing 1 c.c. of the milk 

 diluted 1 : 1000 in physiologic salt solution in a test-tube and 

 allowing a few drops of the immune rabbit serum to flow down the 

 inside wall of the tube. The reaction is positive when a white 

 disk forms at the juncture of the two fluids. The fat should be 

 removed from the milk before dilutions are prepared. 



The Complement-fixation Test (Bauer). — This test is more 

 complicated than the previous one, but can be used with milk in 

 relatively low dilutions, and it is strictly specific. For this test 

 the following material has to be prepared : 



1. Amboceptor Serum. — In each of a series of ten to twelve 

 tubes place 1 c.c. of a 5 per cent, suspension of washed sheep 

 corpuscles and 0.1 c.c. of guinea-pig serum (complement). To 

 the mixture add in falling amounts from 0.01 to 0.0001 c.c. of 

 inactivated amboceptor serum. This is prepared from rabbits 

 injected several times with the 5 per cent, suspension of sheep 

 corpuscles. It is inactivated by heating to 56° C. for thirty 

 minutes. One tube is left without amboceptor serum as control. 

 The amboceptor serum must be suitably diluted with physiologic 

 salt solution in order to obtain the proper quantities. 



After all the tubes have been filled, enough salt solution is 

 added to each one to bring the volumes up to a definite amount. 

 Then all tubes are placed in an incubator at 37° C. and left for 

 two hours. After this time one of the tubes will show which 

 amount of amboceptor serum produces complete hemolysis. 

 Twice this amount is taken as the titer of the serum. It may be 

 kept in a frozen condition for a long time. As a minimum titer 

 for practical use 0.001 to 0.0005 c.c. should be sufficient to produce 

 complete hemolysis with 1 c.c. sheep corpuscles and 0.1 c.c. guinea- 

 pig serum. 



2. Complement. — Place in each of a series of about eight tubes 

 one dose of the amboceptor serum, 1 c.c. suspension of washed 

 sheep corpuscles, and falling amounts of suitably diluted com- 

 plement serum in quantities of from 1 c.c. to 0. Then add enough 



