148 Dr. W. Roberts. Estimation of the Amylolytic [May 5, 



starch mucilage. It should be used fresh, for it is apt to change in a 

 few days, and to lose its opalescent appearance, and slight muculagi- 

 nous consistency. When thus changed it is found to contain sugar. 

 So long as it maintains its slight opalescence and slight mucilagi- 

 nous character it is fit for use. 



The iodine solution used in the testing was composed of 1 part of 

 the Liquor lodi of the British Pharmacopoeia, diluted with 200 parts of 

 water. 



In determining the data on which is based the method of diastasi- 

 metry here proposed, it was necessary to ascertain the mutual relations 

 in regard to the amylolytic process of three factors, namely, the 

 quantity of pancreatic extract set in action, the time required to reach, 

 the achromic point, and the temperature at which the enzymosis was 

 carried on. 



Quantity and Time. — The amount of amylolytic work done by a 

 given sample of pancreatic extract is strictly proportional to the 

 quantity of it set in action — in other words, the amount of the 

 standard starch mucilage which can be changed to the achromic 

 point in a given time and at a given temperature, varies directly 

 as the quantity of the extract employed. This law of proportionality 

 may probably be regarded as fundamentally applicable to the action 

 of all enzymes, which, having no power of growth or multiplica- 

 tion, conform in this respect to the common law which governs the 

 action of ordinary chemical agents. The rule is, however, liable to 

 interference if the products of the enzymosis accumulate in the solu- 

 tion to such a degree as to hamper the action. In the conditions 

 observed in the following experiments this interference did not arise. 

 The starch mucilage operated on was exceedingly dilute, and con- 

 sequently the sugar and dextrines produced in the transformation 

 never accumulated to such a degree as to check the enzymosis. 



In the action of all enzymes the element of time is an essentially 

 important factor. An enzyme liberates its energy gradually, in suc- 

 cessive portions, and it takes a comparatively long time to exhaust 

 itself completely. I found that pancreatic diastase, in the presence of 

 excess of starch mucilage, took not less than forty-eight hours to 

 completely exhaust itself at the temperature of 40° C. — (" Lumleian 

 Lectures" for 1880, " On the Digestive Ferments," p. 38). 



The fundamental rule which governs the mutual relations of quan- 

 tity and time in the action of an enzyme is that of inverse proportion. 

 That is to say, that double the quantity of an enzyme will do a given 

 amount of work in half the time, and that half the quantity will 

 require double the time. This rule, however, is apparently controlled 

 by another rule, namely, that an enzyme liberates its energy at a pro- 

 gressively retarded rate. If we conceive an enzyme as a body in a 

 state of tension, charged with a certain amount of dormant energy, 



