44 
Twice also a series of four experiments with different py was made 
simultaneously with the same Soja extract to make sure, that in all 
the same quantity of enzyme had been brought into solution. 
Evidently the smallness of enzyme concentration involved the 
necessity of long reaction-time. 
In order to investigate, if during such long exposures to these - 
H-ion concentrations at 27° any weakening of the enzyme activity 
had taken place, the remaining parts of the four phosphate-enzy me- 
solutions were left for 24 hours in the bath at 27°. On the next day 
the required experiments were repeated with these ones. 
In this way it became manifest, that the combined action of H-ion 
concentration, temperature and time had here, within the limits of 
experimental errors, no appreciable effect on urease in the acid 
solutions. If, however, at 27° the H-ion concentration was maintai- 
ned beyond the neutral point, the activity of the enzyme decreased 
slowly, but distinctly. In alkaline solutions for the calculation of m, 
as before, only the measurements of the first intervals had to be used. 
The acidity, used in these experiments, had itself no hydrolytic 
action on urea, as was ascertained by boiling samples of 10 c.c. of 
the liquids with py=6,67 and py == 7,52, incubating them for 24 
hours at 27°, adding to each 2 c.c. of 0,06 °/, urea and maintaining 
these mixtures again for 24 hours at 27°. No ammonia was formed. 
The results obtained for the specific urease-activity m of low urease 
concentrations are brought together in fig. 15, in which for the sake 
of comparison the curve of fig. 3 is also reproduced. 
The interpretation of these results, based on the theory, put forward 
in part 9 is the following. 
An enzyme molecule being the centre of two concentric spheres, 
an inner one, in which the substrate is broken down, and an outer 
shell, in which the reverse action is brought about, it is evident, 
that, if the concentration of the enzyme is large enough to make 
the inner spheres intersect each other, there is no place in the solu- 
tion, where the condition for synthesis, that is weakened radiation, is 
realised ; at least, so long as the enzyme has retained its original activity. 
A sufficient dilution of the urease will, however, establish a 
distance between the enzyme-molecules, large enough, to leave the 
outer shell open for the reverse action. The total power of urease 
to convert urea into ammonium carbonate, representing the diffe- 
rence between the hydrolysis and the synthesis it brings about, must 
therefore be expected to be diminished by decreasing the urease 
concentration beyond a certain value. 
The observed facts are clearly in accordance with this theory : 
