114 Prof. H. E. Armstrong and Mr. E. Horton. [Jan. 26, 



In carrying out the experiments, as a rule, the mixtures studied were 

 contained in Jena flasks provided with rubber stoppers. In some cases, 

 when it was thought that ammonia might be lost by volatilisation, the 

 stopper was provided with a short length of glass tubing to which a piece of 

 rubber tubing carrying a screw clip was attached ; the mixture having been 

 introduced, the pressure within the flask was slightly reduced and the clip 

 then screwed up ; at the close of the experiment, by attaching the rubber 

 uibe to the burette and allowing acid to run in, it was possible to prevent 

 any escape of ammonia. In some experiments in which a large number of 

 samples were removed in rapid succession, the mixture was contained in 

 a flask attached to an automatic pipette and the liquid forced up into this 

 latter by air pressure — both flask and pipette being in the incubator and the 

 pressure operated from outside. 



Selective Activity of Urease. — Takeuchi has tested the action of Soja urease 

 on a considerable number of nitrogen compounds, namely alanine, allantoin, 

 arginine, benzamide, glycine, guanine, hippuric acid, histidine, kreatinine, 

 leucine, tyrosine and uric acid ; none of these was affected. He states that 

 biuret is slightly attacked but his figures scarcely justify the conclusion. 



"We have thought it desirable to study the behaviour of substances more 

 closely related to urea and have therefore subjected the various substituted 

 ureas to the action of urease. 



A convenient and striking way of demonstrating the hydrolysis of urea by 

 Soja urease is to place a small quantity of a 5 per cent, solution of urea in 

 a flat glass dish or on a white plate, then to add a drop or two of an alcoholic 

 solution of phenolphthalein and dust in a quantity of the bean meal free 

 from oil or even raw meal. In a very short time, especially if the liquid 

 be slightly warmed, the colourless solution assumes a pink and then a full 

 rose-red colour. If the experiment be made with either methylurea or 

 ethylurea, no such effect is observed. 



In a first series of experiments with various substituted ureas in which 

 solutions of the ureas were digested with the solution of urease and then 

 subjected to distillation with steam, the distillates obtained were so slightly 

 alkaline that it was evident that little if any action had taken place. 

 A second set of observations was then instituted with 2M/5 solutions, 

 prepared at 25°, of methylurea, s-dimethylurea, «s-dimethylurea, ethylurea 

 and s-diethylurea and one of biuret prepared at 35° (as the biuret crystallised 

 out at 25°). 



From each of the solutions, 20 e.c. was measured into each of two 300 c.c. 

 round Jena flasks, one containing 20 c.c. of Soja extract, the other 20 c.c. of 

 water. The 12 flasks containing these mixtures and another containing 



