160 LABORATORY COURSE IN SERUM STUDY 



individuals and tests for increase in antitrypsin have been pro- 

 posed as an aid to diagnosis of carcinoma. The condition, how- 

 ever, is not limited to patients with malignant diseases, but is 

 present also in pernicious anaemia, in Graves' disease, in ad- 

 vanced tuberculosis, and in many other infections. 



A specific antitrypsin which may be quite different in its nature 

 from the substance present in normal serum is developed in re- 

 sponse to injections of trypsin into animals. The precise deter- 

 mination of the antitryptic activity of the serum in experimental 

 work is made by adding serum to mixtures of trypsin and some 

 protein substrate and after incubation comparing the amount of 

 incoagulable nitrogen in the flasks containing serum with the 

 amount in control flasks containing trypsin alone. 



Simpler methods have been devised for clinical use. One 

 widely used consists in placing drops of mixtures of trypsin and 

 serum in varied proportion on the surface of Loeffler's blood serum 

 plates and determining the action of the trypsin by the formation 

 of a pit on the surface of the plate underneath the drop of fluid. 



A more satisfactory method is that of Fuld and Gross as 

 follows : Mixtures of serum with varying concentrations of tryp- 

 sin are allowed to act on an alkaline solution of casein and after 

 incubation the undigested casein is precipitated by the addition 

 of acetic acid. 



Reagents : 



1. Trypsin solution. Dissolve 0.5 gram of trypsin in 50 c.c. of 

 salt solution containing 0.5 c.c. of normal soda. Make up to 500 c.c. 

 with salt solution. Samples of commercial trypsin vary greatly in their 

 activity and this stock solution should be diluted if necessary until the 

 amount required to digest 2 c.c. of casein solution is approximately 

 0.5 c.c. 



2. Casein solution. Dissolve 1 gram of casein in 100 c.c. of N/10 

 NaOH by warming and neutralize the solution with N/10 HC1, using 

 litmus as an indicator. The volume is brought up to 500 c.c. with salt 

 solution and the solution filtered. It should be sterilized in the Arnold 

 sterilizer if it is not to be used immediately. 



3. Acetic acid solution composed of glacial acetic acid 5 c.c., 

 alcohol 45 c.c., water 50 c.c. 



