1881.] and Proteolytic Activity of Pancreatic Extracts. 147 



diastasic solution is to ascertain the amount of sugar produced when a 

 given quantity of the solution is made to act on a given volume of a 

 standard starch mucilage, for a fixed time and at a fixed temperature. 

 This method has already been recognised, by Mr. H. T. Brown and 

 Mr. J. Heron in their paper on the transformation of starch by malt 

 infusions.* Kjeldahl has developed this method to a further point, 

 and has used it to measure the comparative activity of malt infusions 

 and of saliva. f 



In the method about to be described, a simpler and speedier pro- 

 ceeding was employed, and the results were so brought out as to indi- 

 cate absolute as well as comparative values. In principle the method 

 consists in ascertaining the quantity of starch mucilage of known 

 strength which can be transformed, by a unit measure of a diastasic 

 solution, to the point at which it ceases to give a colour reaction with 

 iodine, in a unit of time, and at a fixed temperature. 



"When starch mucilage is treated with extract of pancreas, or with 

 any other diastasic solution, the mixture progressively loses its pro- 

 perty of giving a colour reaction with iodine. First the blue reaction 

 of unaltered starch passes away, then the brown and yellow reactions 

 of dextrine successively disappear. It is not difficult to fix, with a 

 fair amount of accuracy, the vanishing point of this reaction. This 

 point may, for our present purpose, be called the achromic point. 



The extract of pancreas employed in these observations was prepared 

 by digesting fresh pancreas, freed from fat and chopped up, in four 

 times it weight of dilute alcohol, containing 25 per cent, of rectified 

 spirit (sp. gr. 0*838). The digestion was continued for four or five 

 days, with occasional agitation. The mixture was then filtered through 

 paper. Filtration is much facilitated by the addition to the solvent of 

 0'02 per cent, of acetic acid (containing 28 per cent, dry acetic acid). 



The standard starch mucilage was made from potato starch. Owing 

 to the large size of its granules, potato starch is easily obtained in a 

 state of great purity, by repeated levigation with water, and after- 

 wards drying the product at 40° C.J The mucilage was made of the 

 strength of 1 per cent., and in the following manner: 5 grms. of 

 starch were well stirred up into a thin mud with 30 cub. centims. of 

 water, and then pouied in a slender stream into 470 cub. centims. of 

 briskly boiling water. The mixture was stirred and allowed tp boil 

 for a few seconds. Thus prepared the mucilage is perfectly smooth 

 and uniform, and is so diffluent that it can be measured out like an 

 ordinary liquid. This is known in the present paper as the standard 



* " Journal of the Chemical Society," September, 1879. 



f " Compte Bendu des Travaux du Laboratoire de Carlsberg," 1879, p. 129. 



X The so-called pure starch of the sbops is worthless for the purposes of diastasi- 

 metry. A supply of pure potato starch may be obtained from Mottershead & Co., 

 Chemists, Manchester. 



