1131 



Ten test-tubes of Jena-glass, about 20 cm. long and 2.3 cm. wide, 

 had before been placed in the bath. These test-tubes were (as iu 

 VAN Slyke's experimeuts) closed by rubber stoppers with two boriugs. 

 Through oue of these a glass tube passed, about 30 cm. long and 

 4 or 5 m.m. outside diameter, ending near the bottom in a little 

 bulb with pinholes. The second l)oring held a small pipette-like 

 tube, with some cottonwool in the narrow end at the top, which 

 was meant to prevent the passage of any splashes of the liquid 

 with the air-current. 



Each of these test-tubes received 10 c.c. of the extract E. Together 

 with the tubes a flask with 0.150 gram of urea, dissolved in 250 

 c.c. water, was placed in the thermostat. 



After equilibrium of temperature had been established, 2 c.c. of 

 urea solution were introduced in each test-tube with an accurate 

 pipette. Like all the pipettes used in these experiments, this one 

 was calibrated for blowing out one minute after the liquid had run 

 out, which gives the greatest accuracy, provided of course, the 

 inside is cleaned beforehand with a mixture of sulphuric acid and 

 bichromate. A moment's stirring through the long tube with air, 

 freed from carbon dioxide, ensured complete mixing. Both tubes were 

 closed by pieces of rubber tubing and clips. 



The moment the 2 c.c. had run out of the pipette and the con- 

 tents of the test-tube had been provisionally mixed bj shaking, was 

 taken as the starting-point of the enzyme-action. As the 2 c.c. ran 

 out of the pipette in a few seconds this point could be detei-mined 

 with sufficient accuracy. 



In a wooden block with two rows of holes (see Figure 1) the 

 necessary number of thickwalled glass tubes were kept ready, each 

 containing a carefully measured quantity, between 5 and 12 cc, 

 of sulphuric acid Vbo ^^^ '^'^d filled up with water to a height of 

 about 7 cm. These tubes were also closed by a rubber stopper, 

 through which passed a long tube with pinholes and a short oue. 



At the end of the fixed time-interval (or rather about '/< niinutes 

 before it, as this was within a few seconds, the time required for 

 the next operation till the reaction was consideied to have stopped) 

 the test-tube was taken out of the thermostat and put into the 

 wooden block. The rubber tubing B being connected with the glass 

 tube, the cli|) was removed, the closing of the tube .1 was taken 

 off and replaced by a piece of rubbei- tubing, in the open end of 

 which was then put a drop of octylaicohol to pievenl foaming. 

 Immediately after this the point of a pipette with about 25 cc. of saturated 

 potassium carbonate solution was introduced into this rubber tubing 



