FERMENT REACTIONS 309 



Diffusion Tubes. For purposes of dialysis Abderhalden recom- 

 mends parchment tubes prepared by Schleicher and Schiill (No. 597). 

 These may be kept in water covered with toluol and should never 

 be used while dry or without being previously tested for their 

 tightness. To this end a small quantity of normal serum is dialyzed 

 under toluol against distilled water (as described below) for twenty- 

 four hours, when the dialyzate is tested for biuret. Should the 

 reaction be positive it is clear that the tube is not tight enough. 

 Judd found in my laboratory that there are only about six tubes in 

 twenty-five (of the number which Abderhalden recommends) which 

 are serviceable in this respect, the majority permitting the diffusion 

 of proteins w^hich will likewise react with the new triketo reagent, 

 which is usually employed in testing for biuret. On the other hand 

 it is well to test the tubes with a little Witte peptone solution, so as 

 to make sure that they are not too tight. This, however, seems to be 

 rare. 



After use the tubes should be washed in running water, until the 

 surrounding liquid no longer gives the biuret reaction. They are 

 then kept in water under toluol until they are needed again, or, as 

 Judd recommends, they may be suspended in distilled water in the 

 corresponding cylinders, the latter stoppered with cotton, and steril- 

 ized by steam, when they are ready for use. 



The Biuret Test. While fairly satisfactory results may be obtained 

 with the old copper sulphate test, usin^ 5 c.c. of 33 per cent, 

 caustic soda solution for 10 c.c. of the dialyzate, mixing well 

 and superimposing a layer measuring 0.25 to 0.5 cm. of an 0.25 

 per cent, solution of copper sulphate, the triketohydrinden hydrate 

 (Ninhydrin) test is in many respects to be preferred and much more 

 sensitive. For this reason it would not be advisable to use the latter 

 test in the final examination if the less sensitive copper sulphate 

 reaction only has been used in testing the placental tissue for 

 biuret. The triketo reagent is a white crystalline substance, which 

 is employed in a 1 per cent, aqueous solution. On adding 0.2 c.c. 

 of this to a solution of peptone a violet color develops on boiling. 

 (This may be tried with a very dilute solution of Witte peptone.) 



Preparation of the Serum. The blood should be obtained under 

 aseptic precautions and examined as fresh as possible. From 5 to 

 10 c.c. are best withdrawn with a syringe from one of the veins at 

 the bend of the elbow. The serum is separated from the corpuscles 

 by centrifugation in the usual manner. 



