156 



Dr.. W. Roberts. Estimation of the Amylolytic [May 5 r 



Time. 

 6 minutes 



More pronounced curdling. 

 Pronounced curdling. 

 Diminished curdling. 

 Slight curdling. 



~No change; vanishing point of the metacasein 



Reaction on boiling. 



10 to 80 



90 

 95 

 100 



?5 



reaction. 



The length of time during which the successive steps of the transfor- 

 mation may continue observable depends on the energy of the action ; 

 and this, in its turn, depends on the activity of the preparation and 

 the quantity of it added to the milk ; it is also greatly influenced by 

 temperature. By using an excess of an active pancreatic extract, and 

 with a favourable temperature, all the steps of the process may be 

 crowded almost into an instant of time ; with converse conditions the 

 action may linger on for many hours. 



Although milk is a secretion of somewhat variable composition, the 

 oscillations which it exhibits, when it is the product of a dairy, and is 

 not intentionally adulterated, do not materially vitiate it for the 

 purposes of a test fluid such as is here required. The milk delivered 

 at my house presented very little variation. It had a density of 1030 

 — seldom varying more than a degree from this point — and the results- 

 obtained with the milk of different days showed a remarkable uni- 

 formity. Milk from different dairies, and at different seasons of the 

 year, would no doubt present greater irregularities. Milk should, 

 however, be used fresh, for if it have become slightly acid, as it is apt 

 to do in keeping, the results obtained are untrustworthy. 



If milk be diluted with water the occurrence of the metacasein 

 reaction is postponed ; and the degree of postponement varies with the 

 degree of dilution. For example, if 50 cub. centims of pure milk are 

 changed to the onset point of the metacasein reaction in three minutes, 

 the same quantity of milk diluted with an equal volume of water will 

 take six minutes to reach the same point — other conditions being equal. 

 There are, however, several advantages in using diluted milk instead of 

 pure milk as the experimental fluid. The inequalities of the milk are n 

 thereby minimised. The ''strike" of the reaction is more sharply 

 defined, and the required quantity of pancreatic extract can be 

 included in the water of dilution. This last is an important advantage, 

 because if the extract to be tested is feeble, a considerable quantity of it 

 requires to be added, and this, if pure milk were employed, would 

 seriously alter its degree of dilution, and thereby vitiate the results. 

 In the following experiments, milk diluted with an equal bulk of water 

 was invariably employed ; and if the quantity of pancreatic extract to 

 be added exceeded 3 cub. centims. for every 50 cub. centims. of milk, 

 this was always included in the water of dilution. 



In principle the method of trypsimetry here proposed consists in 



