104 THE TOXINS OF THE HIGHER PLANTS AND ANIMALS 



c.cm. of a 2 per cent, dilution of the serum for examination; to these is next added the 

 trypsin solution in successively increasing amounts, beginning with the smallest quan- 

 tity which in the first part of the test was sufficient to completely digest the given 

 amount of casein. Salt solution is then added to each of the test-tubes so that all con- 

 tain an equal quantity of fluid, and the mixtures placed in an incubator at 37 C. for 

 one-half hour. At the end of this time, several drops of the acid are added to each tube. 

 Those tubes which become cloudy or show a precipitate designate the amounts of 

 trypsin solution which have been neutralized by the 0.5 c.cm. of diluted serum. For 

 example: 



In the first part of the test it was found that the tube containing 0.4 c.cm. of trypsin 

 was the first to remain clear, in other words was sufficient to fully digest 2 c.cm. of 

 the casein solution. In the second part of the test the lower limit of the added trypsin 

 dilution was 0.4, and it was found that the tubes containing 0.4, 0.5, 0.6, and 0.7 c.cm. 

 of trypsin, for example, now gave precipitates and only 0.8 remained clear. This 

 indicates that part of the formerly sufficient amount of trypsin was now neutralized 

 by the antitrypsin of the added serum so that digestion was interfered with. Thus 

 the antitrypsin titer in this case is 0.8. 



Recently the above method of trypsin titration has been applied to the determina- 

 tion of the presence of pancreatic ferment in the intestinal secretions, feces, and stomach 

 contents. 



