268 FERMENTS AND ANTIFERMENTS 



Owing to the fact that it gives a blue color in the presence of any 

 compound that possesses an amino-group in the alpha position of the 

 carboxyl group, it is of great value as an aid in recognizing the products 

 of protein digestion (Fig. 77). 



Testing the Shell for Non-permeability to Albumin. 1. New shells 

 should be softened by soaking them for half an hour in sterile distilled 

 water. A dozen or more may be tested at one time. 



2. The albumin solution is prepared by placing 5 c.c. of the albu- 

 min of fresh eggs in a mixing cylinder, and adding distilled water to 

 make 100 c.c. Mix well. There must be no flakes. Instead, a clear, 

 hemoglobin-free serum which has been dialyzed against running water 

 to remove dialyzable substances, may be used in doses of 2.5 c.c. for 

 each shell. 



3. Carefully pipet 5 c.c. of the albumin solution into each shell. 

 Great care should be exercised that none of the solution contaminates 

 the outside of the shell. The preferable method is to hold the shell with 

 a pair of broad-toothed sterilized forceps and carry the pipet to the 

 bottom, in order that none of the albumin should contaminate the upper 

 portion of the inside of the shell. The pipet may easily touch the edge 

 of the shell and thus contaminate the dialysate. If in doubt, cover the 

 upper end of the shell with the forceps and wash the outside with running 

 water. 



4. The loaded shell is now placed in a sterile dialyzing cylinder con- 

 taining 20 c.c. of sterile distilled water. Never load the shell in this 

 cylinder, for some of the albumin may fall into the distilled water. 



5. Cover the contents of the -shell and the surrounding distilled water 

 with a layer of toluol about J mch m depth. Replace the cotton plug 

 in the cylinder. 



6. Incubate at 37 C. for sixteen hours. 



7. Pass a sterile pipet quickly through the layer of toluol and remove 

 10 c.c. of the dialysate to a clean sterile test-tube, and test for albumin 

 by the biuret reaction. Add 2.5 c.c. of a 33 per cent, solution of sodium 

 hydroxid; shake gently, but remove the thumb from the top of the tube. 

 The solution may become slightly cloudy. Carefully overlay with 1 c.c. 

 of a 0.2 per cent, solution of copper sulphate in such manner that a sharp 

 line of demarcation separates the alkaline dialysate from the copper 

 sulphate solution. A delicate violet tint at this line indicates that al- 

 bumin is present and that the shell is useless. If one cannot see this 

 color or is in doubt, it is well to make the ninhydrin test. To do this 

 dialysis should be continued for twenty-four hours; ninhydrin reacts 



