STARCH 151 



reason, the precipitate has been described as artificial starch. 

 The change is retarded by keeping the paste at 60°. According 

 to Fernbach and Wolff * green malt contains an enzyme 

 " amylocoagulase " which can accelerate the change described. 

 The precipitate is insoluble in hot water and its formation is 

 due to a dehydration and aggregation of the coUoidally sus- 

 pended particles of the original solution ; certain it is that the 

 change is influenced by the presence of electrolytes.^ 



In order to facilitate the preparation of starch solution for 

 indicator purposes, a number of so-called " soluble starches " 

 have been prepared. These are in reality starch which has 

 been treated in a variety of ways by chemicals whereby it is 

 rendered more soluble, without having suffered a sufficiently 

 profound change to influence its ability to give a blue colour 

 with iodine. Lintner's soluble starch is prepared by exposing 

 starch to the action of 7-5 per cent hydrochloric acid for a 

 week and then washing with cold water until free from acid. 



The Composition of the Starch Grain. 



Nageli % was the first to suggest that the starch grain was 

 made up of two distinct constituents, but some years elapsed 

 before his views were supported by reliable chemical evidence. 

 In view of the fact that the terminology employed by the 

 earlier investigators was irregular, a brief historical resume 

 is desirable before considering the present state of our know- 

 ledge of the subject. 



The researches of Nageli have shown that when starch is 

 treated with dilute hydrochloric acid, malt extract, or saliva, 

 a considerable portion goes into solution, leaving a transparent 

 skeleton undissolved. The soluble portion, which gives a 

 blue colour with iodine, Nageli regarded as the true starch 

 constituent of the granule, and named it granulose ; on the 

 other hand, the undissolved skeleton, which he described as 

 not turning blue with iodine (see below), he considered to be 

 of a cellulose nature, and called it starch cellulose or amylo- 

 cellulose. 



* Fernbach and Wolff : " Ann. Inst. Pasteur," 1904, 18, 165. 

 t Samec : " Kolloidchem. Beihefte.." 1912, 3, 123. 

 4: Nageli : " Die Starkekorner," Zurich. 1858. 



