RE LA TIVE A CTIVITY OF DIGESTIVE SOL UTIONS. 3 2 3 



warmed to 40 C. ; a known volume of the diastatic solution to be tested is 

 next added, say 1 c.c., noting the time; drops of the solution 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 noted. By altering the amount of diastatic solution 

 added, as a result of preliminary experiment, this time must be arranged to lie 

 between four and six minutes ; if the time is shorter than four minutes, an 

 error of a few seconds in determining the time of conversion makes too large a 

 percentage error, or if it be much longer than six minutes the transition is too 

 gradual at the end for the eye to accurately catch the achromic point. If v 

 be 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 denned then, D = 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 be 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 J 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. 



Bruckes l 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, 1885, Aufl. 4, Bd. i. S. 311. 



