190 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



shells, thinner than in the corn, and with pitted surfaces and cracks around the edge, 

 much like the openings of oyster shells. At the end of 38 hours the arrowroot and some 

 potato grains showed surface erosions. Some of the potato grains showed change at the 

 small end, this part not reacting with iodine, while the remaining part stained a deep blue. 



BOILED STARCHES. 



The results obtained by various investigators in their digestion experiments with boiled 

 starch are quite as conflicting as those with raw starch. It has long been beUeved that 

 certain kinds of boiled starches are more digestible than others, and it is owing chiefly or 

 solely to this that aiTowroot starch is given preference by the physician over other starches 

 in infant feeding and in the diet of the sick-room. Its superior qualities, however, as will 

 be noted from the following pages, are not owing to the factor of digestibility, but to the 

 absence of certain contaminations wMch render certain other starches of commerce, nota- 

 bly potato starch, unpalatable. In a word, all kinds of boiled starches as ordinarily pre- 

 pared and subjected to the same conditions of expermient are of equal digestibility and 

 yield the same products, quantitatively and quaUtatively. 



In the experiments by Hammarsten (loc. cit.) with saliva on normal raw starch there 

 were material variations in the time of the formation of sugar in the case of different 

 kinds of starch, the interval ranging from 2 to 3 minutes to the other extreme of 2 to 4 

 hours. "Wlien, however, the grains were comminuted by chewing, which is equivalent, 

 as pre^'iously shown, to partial or complete gelatinization in proportion to the degree of 

 comminution, sugar was formed in all of the starches in 1 to 4 minutes. Starch-pastes 

 were found by Hammarsten to show no difference in sugar-forming time. Levberg 

 (Inaug. Disser., St. Petersburg, 1874; Ber. d. d. chem. Gesellsch., 1874, x, 76) gives the 

 order of digestibility of boiled starches, as determined by the quantity of glucose, as 

 follows : Arro^ATOot, potato, wheat, and rice — the first being the most digestible. He made 

 one series of experiments in which he determined the quantity of glucose formed when 

 given quantities of saliva and starch were used. With 9 c.c. of saliva he obtained from 

 potato 60.3 per cent and from arrowi'oot 59.62 per cent; with 10 c.c. of saliva he records 

 from rice 55.76 per cent; and with 16 c.c. of saliva with wheat starch the yield was 62.87 

 per cent. In other observations he found, with standard quantities of saliva and starch, 

 that the maximum results were recorded as follows: Arrowi-oot 8 hours, potato 9 hours, 

 wheat 12 hours, and rice 14 hours. Salomon (.Jour. f. prakt. Chemie, 1882, xxvi, 324), upon 

 the basis of the amount of sugar formed by the digestion of potato and rice starches, found 

 that these starches are identical in degree of digestibility. 



O'SuUivan (Jour. Chem. Soc. Trans., 1878, ii, 141) conducted most of his experiments 

 with potato starch. In liis earUer experiments he satisfied himself that different boiled 

 starches (potato, rice, wheat, corn, etc.) give the same results, quantitatively and quali- 

 tatively, but in a comparatively recent article (Proc. Chem. Soc. Trans., 1904, xc, 65), 

 in which he reports the results of six series of experiments with potato, malt, barley, corn, 

 and rice starches, using extract of malt or diastase, it is stated that the percentages of 

 dextrin and maltose yielded by potato starch do not correspond M'ith those recorded with 

 the other starches, and therefore that the products of potato starch can not be taken to 

 indicate the products of the other starches. It has since been fouiid that the difference 

 noted by O'SuUivan is due to errors of experiment (see Ford, page 193). 



The digestibility of all kinds of starch is stated by Butyozin (Inaug. Dissert., St. 

 Petersburg, 1887) to be increased by the length of time they are boiled, and that under 

 given conditions the starches of millet, buckwheat, rice, and peas show ease of digestibility 

 in the order given. In opposition to this author. Day {loc. cit.) records that potato, aiTow- 

 root, and probably tapioca and sago starch-pastes are not rendered more digestible by 

 prolonged cooking; and in confirmation, that cereal starches (wheat, corn, rice, barley) 



