326 IMMUNOLOGICAL METHODS OF DIAGNOSIS 



be used while dry or without being previously tested for their tight- 

 ness. To this end each tube is charged with 1 c.c. of a 1 per cent, 

 solution of silk peptone, under toluol, and dialyzed at body tem- 

 perature against 20 c.c. of water (under toluol) for from twenty- 

 four to sixty-six hours, according to the thickness of the dialyzer, 

 when those tubes are rejected which failed to let the peptone pass 

 (as tested with ninhydrin). The remaining tubes are then tested 

 (after thorough washing), after being charged with 1 c.c. of normal 

 human serum, and those discarded which are found to be permeable 

 for proteins. Judd found that there are only about six tubes in 

 twenty-five (of the number which Abderhalden originally recom- 

 mended) which are serviceable in this respect, the majority permitting 

 the diffusion of proteins which will likewise react with ninhydrin. 

 This difficulty has been recognized by the manufacturers of the 

 parchment thimbles, and a tighter tube, No. 597A, has hence been 

 placed upon the market. So far as my personal experience goes, 

 none of the new tubes which have been sent to the United States 

 allow of the passage of sufficient quantities of reacting substances 

 within twenty-four hours, the time limit of the Germans, but may 

 still be used if the incubation is continued for sixty hours or even 

 longer. The failure on the part of the manufacturers to give some 

 indication of this excessive tightness is no doubt responsible for 

 many disappointments and adverse criticisms, which the Abder- 

 halden method has met with in this country. A tested dialyzing 

 tube is at present marketed by R. Schoeps, of Halle, but has in my 

 experience no advantage over the others. 



After use, the tubes should be washed for several hours in running 

 water. They are then kept in water under toluol until they are 

 needed. 



The Biuret Test. While Abderhalden originally advocated the 

 use of the old copper-sulphate test as well, he now demands 

 the ninhydrin test, and probably all workers at present are making 

 use of this exclusively. It is much more sensitive than the other. 

 For this reason it should be borne in mind that 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 reagent (triketohydrinden hydrate) 

 is a white crystalline substance, which is employed in a 1 per cent, 

 aqueous solution. In testing the tissue this is used as described 



