RELA TIVE A CTIVITY OF DIGESTIVE SOL UTIONS. 325 



of 19 c.c. of water and 1 c.c. of glycerin-carmine solution. In this manner 

 ten standard tints are obtained, the values of which correspond to the numbers 

 1 to 10; these are mounted in a stand against a uniform white background, 

 and are used to compare with the results of digestion, after equal intervals 

 of time. For example, if after thirty minutes' digestion the tint of one test 

 tube corresponds most closely to that of Standard 2, while that of another 

 corresponds to Standard 6, the latter is three times as powerful a digestive 

 solution as the former. The digestive solutions should be so diluted that they 

 act somewhat slowly, because after a time a maximum tint obtains, and then 

 the weaker digestive fluid catches up on the other ; the farther apart from 

 this maximum the measurements are taken the better. Also, if a close approxi- 

 mation to the comparative amounts of pepsin in two solutions is required, 

 after a preliminary experiment the stronger of the two must be diluted 

 experimentally until its 'action is equal to that of the other, then the pro- 

 portion of dilution gives the proportionate strength in pepsin of the two 

 solutions. This determination may be most speedily attained by making a 

 simultaneous series of dilutions of the stronger solution, and comparing the 

 strength of their action with that of the other solution or a series made 

 from it. 



Two tubes of equal speed of action are picked out, and from their dilutions 

 the comparative richness in pepsin of the original fluid easily follows. Griitzner's 

 method may also be employed without a scale of standard tints, by stopping 

 digestion after an equal period, and then diluting the stronger solution until 

 its tint becomes equal to that of the weaker, or by carrying out two series 

 in aliquot dilution of the two solutions to be compared, and picking out 

 equally advanced members of the two series. In case the comparison is made 

 with solutions of unequal power, it must be remembered that what is measured 

 is the comparative digestive power and not the comparative strength of the 

 solutions in pepsin, because the two are not proportional; 1 in all 'cases it is 

 preferable, for accuracy, to prepare solutions from the originals of equal power, 

 and from the amount of dilutions of these to deduce the comparative strength 

 in pepsin of the originals, as indicated above. 



Mette's method. 2 This method is stated by Samojloff to yield exact 

 results. It consists in filling fine glass tubes of 1 to 2 mm. in diameter with 

 fluid white of egg, then coagulating by heat, and cutting off pieces of equal 

 length. These are placed in the digestive solutions at body temperature, and, 

 after the lapse of a certain interval, the length of white of egg digested off is 

 measured, which gives a measure for the comparative activities of the two 

 fluids. 



Griitzner 3 has also introduced methods for comparing the diastatic 

 and fat-splitting powers of pancreatic extracts. 



That for diastatic action closely resembles Griinhagen's method for proteo- 

 lytic action. Equal volumes of 3-4 per cent, starch paste are placed on similar 

 filters, through which they do not filter until dissolved; to each filter 0'2 to 

 0'3 c.c. of the extracts to be compared are next added, when solution of the 

 starch takes place at a rate proportional to the amount of enzyme present, 

 and a comparison of the amounts filtering through in a given time supplies 

 a measure for the activities of the extracts. 



The method of comparing the fat-splitting powers of different extracts 

 consists in allowing the extracts to act on an emulsion in presence of litmus, 

 and noticing the time and amount to which the latter is turned red by the 

 acid developed. The emulsion recommended is made by mixing 10 parts of 



1 See Schiitz's law, p. 322. 



2 Samojloff, Arch, de sc. IrioL, St. Petersbourg, 1893, tome ii. p. 707. 



3 Arch.f. d. ges. PhysioL, Bonn, 1876, Bd. xii. S. 293, 303. 



