346 
Proceedings of the Royal Society of Edinburgh. [Sess. 
3. Formol. — In these experiments Schering’s preparation has been used. 
The method of procedure was as follows : — 
The pepton solution was measured out into dry flasks with the material 
to be tested. If an alkaline medium is desired, a definite quantity of 
sodium carbonate or bicarbonate may be added to the pepton solution 
beforehand, or the alkali may be used in extracting the enzyme. In 
these experiments a concentration of sodium bicarbonate equal to 1 per 
cent, has been employed. 
In the preliminary experiments an enzymatic solution was used, which 
was obtained by extracting pancreatin with water in proportions varying 
from to yoVo- Apart from the difficulties attending filtration, it was 
found that only a very small amount of the enzyme went into solution, 
even when relatively large quantities of water were used. It was, moreover, 
repeatedly observed that it was impossible, by filtration through paper, 
to obtain a solution which was quite homogeneous as regards activity. 
It was therefore decided to weigh out the desired quantity of pancreatin 
directly into each flask used in the experiment. 
During digestion the development of micro-organisms has been pre- 
vented by the presence of chloroform. Originally, a few drops were added 
in each case before digestion. This method, however, was discarded owing 
to the possible retarding influence o£ excess chloroform. It was found 
quite sufficient to saturate the pepton beforehand by shaking with excess 
of chloroform, while in this way the presence of excess during digestion 
was avoided. In those cases where a liquid extract of the enzyme was 
used, it was also saturated before digestion. 
The digestions have been performed in stoppered flasks which were kept 
at 40° C. in an incubator or a water-bath. The time of digestion has been 
regulated according to the activity of the enzyme. Abderhalden has, in his 
experiments, found an incubation of a few hours sufficient to produce a 
weighable quantity of tyrosin, but, when working with smaller degrees 
of enzymatic activity, a more prolonged digestion is necessary. From 
observation of the reaction it would appear that the separation of the 
tyrosin is by no means an immediate process. Apparently, during the 
first period of decomposition, soluble products only are produced, no deposit 
being visible for some time. Eventually, tyrosin begins to crystallise out, 
and, once commenced, the process goes on rapidly. In one series of 
digestions the material remained clear after twenty hours’ incubation. At 
the end of twenty-three hours, however, a considerable deposit was found 
in all the flasks. 
After digestion the flasks were cooled in water for a few minutes and 
