RE LATH '/: . 1 CT1 VITY OF DIG ES 1 7 VE SOL UT70NS. 3 2 3 
warmed to LO C. \ a known volume of the diastatic solution to be tested is 
next added, say 1 c.c, uoting the time: drops of the Bolution are then tested 
from time to time, say at intervals of ten seconds, with drops of iodine on a 
porcelain slab until no yellow tinge is produced, and the interval of time 
which has elapsed is uoted. By altering the amount of diastatic solution 
added, as a result of preliminary experiment, this time must he arranged to lie 
between four and six minutes; if the time is shorter than four minutes, an 
error of a few second-; in determining the time of conversion makes too large a 
percentage error, or if it he much longer than six minutes the transition is too 
gradual at the end for the eye to accurately catch the achromia point. If v 
he the volume in cubic centimetres of diastatic solution added, n the time to 
reach the achromic point in minutes, and D the diastatic value of the solution 
10 5 
as above defined — then, Z)= — x — 
v n 
This value of D gives a measure of the activity of a given diastatic solution, 
in terms of a standard which can he easily reproduced at any time to measure 
the activity of another diastatic solution, and so comparable results may be 
obtained. 
Various methods are in use for determining the relative activity of 
proteolytic solutions. 
The earliest method is that first introduced by Bidder and Schmidt, and 
used in various modifications by other experimenters. It consists in deter- 
mining the weight of proteid dissolved in equal times, by equal volumes of the 
digestive liquids added to equal volumes of a proper digestive medium. The 
method is oftenest used for relative determinations of pepsin, when the 
medium used is hydrochloric acid solution of 1 or 2 per mille, but it may also 
be used for trypsin, when \ per cent, sodium carbonate can be used as a 
medium. The digestive solutions are placed in a bath at 40° C, and when 
they have acquired the temperature of the bath, equal weighed portions of 
equally finely subdivided hard-boiled white of egg (obtained by passing through 
gauze netting) are added to each, and digestion allowed to proceed for the same 
period in each case, say twenty-four hours ; the liquids are then filtered, and the 
residues left undigested are washed, dried, and weighed ; a third equal quantity 
of the white of egg used is also dried and weighed without previous digestion ; 
and from the figures so obtained the amounts of dissolved white of egg are 
deduced, and these are taken as representing the comparative peptonising 
values of the two samples. 
Briicke's 1 method. — This method consists essentially in diluting the 
two proteolytic solutions to be compared with the same medium (1 per 
mille HC1) in two series, and then picking out those two members in 
each series which are most nearly equal ; from the relative dilution of 
these two the comparative activity of the two original solutions easily 
follows. 
Vessels. Pepsin Solution of Acidity, Water of Acidity, 
1 per Mille. 1 per Mille. 
1 . . 16 
2 . . 8 8 
3 . . 4 12 
4 . . 2 14 
5 . . 1 15 
6 . . 0-5 15-5 
7 . . 0-25 15-75 
1 " Vorlesungen ueber Physiologie," Wien, 18S5, Aufl. 4, Bd. i. S. 311. 
