SUMMARY OF THE MORE IMPORTANT LITERATURE UP TO 1872. 85 



ment. He believed that these two parts differ in chemical composition, one being soluble 

 and staining blue with iodine and the other being insoluble and not yielding the blue reac- 

 tion with iodine; which difference he thought due to the presence of an unstable inner sub- 

 stance, or gum, which is expelled on heating and which is soluble in cold water. 



The following year Raspail's assertions were disputed by Caventou (Aim. de cliim., 

 1S2G, XXXI, 358), who states that the starch-grain as a whole is stained with iodine, and 

 that raw starch does not contain any part that is soluble in cold water. He also found 

 that the amidine of De Saussure could be extracted from fresh starch-paste by cold water, 

 and that it was merely a modified starch (amidon modifi6). 



Several years later Guibourt (Ann. de chim. et phys., 1826, xl, 183), in support of 

 Caventou, ascertained that both the outer coat and the internal substance stain with 

 iodine, and therefore that they are not of different chemical composition, as held by Ras- 

 pail. He also recorded that when broken-up starch-grains are placed in cold water the 

 inner substance of the grains is dissolved, leaving the integuments. This soluble substance 

 he states is not a gum, and he notes that it gives a blue reaction with iodine. He identi- 

 fied it with De Saussure's amidine, and also with the soluble part of the starch, or the 

 gum, referred to by Raspail. Guibourt's results were confirmed by Berzelius the next year. 

 In 1831 the very important discovery was made by Leuchs (Ann. de chim. et phys., 1831, 

 XXII, 105, G23) that saliva, Uke the aqueous extract of germinating barley, contains a sub- 

 stance that saccharifies starch-paste. This was confirmed by Schwann (Ann. de chim. et 

 phys., 1837, xxxviii, 358) and other observers, and although it was conceded by the author- 

 ities of the day that saliva had tliis property, it was believed that because of the watery 

 character of the secretion the functions of saliva must be in connection with mastication, 

 gustation, and deglutition, and that its saccharifying property could not be of importance in 

 the Hving organism (Wagner's Handworterbuch d. Physiologie, Verdauung, iii, Hfte. i,768). 



The nature of the gum produced when raw starch is subjected to dry heat and when 

 boiled starch is subjected to weak acids or to an aqueous extract of barley, etc., was made 

 a special study by Biot and Persoz {Ann. d chim. et phys., 1833, lii, 72), who prepared 

 this substance by means of dilute sulphuric acid. They beheved that it is not a product of 

 decomposition, but the inner substance of the starch-grain, that is set free by the bursting 

 of the outer coat. Polariscopic examination showed it to be dextro-rotatory, on account of 

 which they gave it the name of dextrin, which name has continued in use to the present time. 



During the next year Raspail {Nouveau systeme de chimie organique) recorded liis earlier 

 views on the structm-e and reactions of starch and reports the results of further studies, 

 which led liim to the conclusion that the substance contained within the integument is 

 dextrin, and that the body which stains blue with iodine is an unknown, unstable prin- 

 ciple. This conclusion was based on the fact that the part of the grain that is dissolved in 

 boiling water is no longer stained blue with iodine, as is also the case with the integuments. 



An investigation of fundamental importance was carried out at this time by Payen 

 and Persoz (Ann. de chim. et phys., 1834, liii, 730), who prepared from germinating 

 barley and other grains, and also from potatoes, a substance which converts starch into 

 dextrin and sugar. They believed that dextrin constitutes the inner substance of the 

 starch-grain and that their prepared substance has the remarkable property of separating 

 the integument of the grain from the inclosed dextrin. Because of this property they 

 named it diastase, from the Greek hidaraaig, meaning separation. They differentiated 

 the processes of dextrinization and saccharification, and they believed that the formation 

 of sugar is a subsequent and not a coincident process in the production of dextrin. It is 

 recorded that when 100 parts of starch, 400 parts of water, and 5 to 10 parts of dried malt 

 are heated to 75° for 3 hours, the dextrin liberated from its integuments is transformed into 

 a sugary substance, and when the preparation was heated to boiling-point the formation 

 of sugar was prevented, because at this temperature, they state, the diastase is destroyed. 



