114 
Proceedings of the Royal Society of Edinburgh. [Sess. 
out, ground with sand and a 1 per cent, solution of Pepton Roche, filtered, 
and the filtrates digested at 37° C., 1 per cent, chloroform being added. 
This procedure was also followed out with the residues and with a sample 
of the whole seed. In each of these cases, as before, a number of the 
digestions were allowed to remain neutral, while others were acidified and 
made alkaline respectively. An entirely negative result was obtained from 
these experiments also. 
The experiments described above were repeated several times with 
different samples of material, the digestions were carried out within a wide 
temperature range (15°, 25°, 37°, 50°), and the period of incubation was 
extended to as much as three weeks. It thus became obvious that an 
invariable negative result could not be due to any accident, but to the 
absence of a peptase capable of splitting off tyrosin from Pepton Roche. 
It was therefore decided to carry through a final experiment in order 
to investigate the matter fully. 
For this purpose a sample of germinating barley was ground up in a 
mincer, extracted for twenty-four hours with chloroform water, and pressed 
in a hand-press. The liquid was freed from suspended particles by means 
of a centrifuge. This extract will, in the following pages, be referred to as 
Extract A. 
The residue from the press was then ground with sand and kieselguhr, 
with the addition of a little water, in the Buchner mortar, and then subjected 
to a pressure of 300 kg. per sq. cm. in the Buchner hydraulic press. The 
liquid obtained in this way, and freed from solid matter as before, will be 
referred to as Extract B. 
Twelve flasks were made up, each containing 5 c.c. 20 per cent. Pepton 
Roche solution and 5 c.c. Extract A, while another twelve were similarly 
prepared with Extract B, T c.c. chloroform being added to each as anti- 
septic. Three of each series were digested at each of the following 
temperatures — 15°, 25°, 37°, 50°. At the same time a similar number of 
flasks containing 5 c.c. 10 per cent. Pepton Witte solution instead of the 
Pepton Roche were placed at the same temperatures, a series of controls 
being prepared for the latter experiment by precipitating the material at 
once with excess of tannic acid. The digestions were examined from day 
to day, and whenever a deposit was found it was filtered off and the 
identity of the tyrosin established by means of Morner’s reaction, the corre- 
sponding Pepton Witte digestions being precipitated with tannic acid at the 
same time. 
The first deposits of tyrosin were produced within six days in the diges- 
tions containing Extract B, at 25° and 37° respectively; the next ones 
