FERMENT REACTIONS 325 



from the tissue no longer gives a reaction with one of the standard 

 tests for occult blood. Unless this point is reached, i. e., unless 

 every trace of blood has been removed the material will be of no 

 value, as the serum of practically every individual reacts with 

 blood and would hence give a positive reaction. 



After the desired degree of purity has been reached the tissue 

 is placed in boiling w T ater w r hich has been slightly acidified with 

 acetic acid (2 drops of the glacial acid to a liter of water) and boiled 

 for five minutes. The supernatant fluid is decanted, replaced by a 

 corresponding quantity of water and the tissue boiled for another 

 period of five minutes. This process is repeated until the water 

 used in the extractions no longer gives the biuret reaction with 

 ninhydrin (see below) even in considerable concentration, in the 

 presence of an excess of the reagent and on standing for a full half- 

 hour. To this end it will be found advantageous to test 10 c.c. of 

 the wash water (after filtering through a hardened filter) from time 

 to time with 0.2 c.c. of the reagent (boiling for just one minute), 

 until no blue color develops on standing. After this point has been 

 reached the total bulk of the tissue is boiled for five minutes with 

 only five times its bulk of water, when 5 c.c. of the filtrate are boiled 

 for one minute with a whole cubic centimeter of the ninhydrin. If 

 then not the slightest shade of blue has developed at the expiration 

 of half an hour the tissue is in proper condition to be used. It may 

 then be stored in a small volume of its last wash water, between a 

 layer of chloroform and toluol, but should be tested again before 

 actual use, and reextracted, if necessary, until the first "accentuated" 

 test, just described, shows the absence of substances which react 

 with ninhydrin. Unless this point is reached a non-specific reaction 

 might be obtained in the actual experiment which would be the 

 outcome not of a digestive action upon the placental protein on the 

 part of a proteolytic ferment in the serum, but of the summation 

 of reacting substances in the serum and tissue, which individually 

 would be insufficient in quantity to cause a color reaction, but which 

 combinedly might do so. 



The tissue therefore must be absolutely free from blood and of 

 soluble substances which might react with ninhydrin. 



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 w y ith toluol and should never 



