336 HAND-BOOK OF PHYSIOLOGY. 



glucose. They add a molecule of water, and may be called hydrolytic. 

 The probable reaction is as follows: 



3 C 6 H 10 3 + 3 H 20 = C 6 H 12 6 + H 10 0. - 3 H 12 6 



Starch Water Glucose Dextrin Glucose. 



This shows that there is an intermediate reaction, the starch being 

 first turned only partly into glucose and principally into dextrin, which 

 is afterward further converted into glucose. The principal amylolytic 

 ferments are Ptyalin, found in the saliva, and a ferment, probably dis- 

 tinct in the pancreatic juice, called Amylopsin. These both act in an 

 alkaline medium. Amylolytic ferments have been found in the blood 

 and elsewhere. 



Conversion of starch into sugar. With reference to the action of the 

 amylolytic ferments, recent observations have shown that the starch mole- 

 cule is not by any means so simple as it has been represented above. As 

 it is said that starchy materials, in the form of wheat and other cereals, 

 and in the potato or its substitutes, form two-thirds of the total food of 

 man, it is very important that we should note (1) the changes which 

 occur in starch on cooking, and (2) the series of reactions it undergoes 

 during its conversion by the amylolytic ferments into sugar. 



(1.) The object of this change is to produce gelatinous or soluble 

 starch. A starch granule consists of two parts: an envelope of cellulose, 

 which gives a blue color with iodine on addition of sulphuric acid, and of 

 qranulose, which is contained within it, giving a blue with iodine alone. 

 Briicke states that a third body is contained in the granule, which gives 

 a red with iodine, viz., erytliro-granulose. On boiling, the granulose 

 swells up, bursts the envelope, and the whole granule is more or less 

 completely converted into a paste or into mucilaginous gruel. 



(2.) Changes which occur on addition of an amylolytic ferment. On 

 the addition of saliva or extract of pancreas to gelatinous starch, the first 

 change noticed is that the paste liquifies very quickly, but the liquid does 

 not give the reaction for dextrin or for sugar; but soon this latter reaction 

 appears, increasing very considerably and quickly, although at first, in 

 addition, a reaction of erethrodextrin, a red on addition of iodine, is 

 found; as the sugar increases, however, this disappears. At first the 

 erythrodextrin is mixed with starch, as the reaction is a reddish purple 

 with iodine, then it is a pure red, and finally a yellowish brown. As the 

 sugar continues to increase the reaction with iodine disappears, but it is 

 said that dextrin is still present in the form of achroo-dextrines, which 

 give no reaction with iodine. However long the reaction goes on, it is 

 unlikely that all the dextrin becomes sugar. 



Next with regard to the kind of sugar formed, it is, at first at any 

 rate, not glucose but maltose, the formula for which is 1? H 22 O n . Maltose 

 is allied to saccharose or cane sugar more nearly than to glucose; it is 

 crystalline; its solution has the property of polarizing light to a greater 

 degree than solutions of glucose; is not so sweet, and reduces copper 

 sulphate less easily. It can be converted into glucose by boiling with' 

 dilute acids. 



According to Brown and Heron the reactions may be represented 

 thus: 



