CHAP. I.] MALTOSE. 47 



one hand incomplete and falls far short of the activity of the removal 

 existing in normal digestion, for it is dependent merely upon the 

 diffusibility of the products.' In the body, on the other hand, we 

 have now every reason for regarding the absorption of products as 

 dependent primarily upon a specific selective activity of the epithelium 

 lining the alimentary canal, and not merely upon the physical 

 properties of the substances to be absorbed. So far, however, as 

 diffusion is the only obvious means at our disposal for removing the 

 digestive products, the dialyser above described is extremely effi- 

 cient 1 ." 



The Sugar which results from the action of Saliva on Starch, 



MALTOSE. 



However large the quantity of diastatic enzyme present in a 

 starch solution and however favourable the circumstances, under 

 ordinary circumstances, in vitro, the conversion into maltose does not 

 proceed beyond a certain point. The tendency of all such transfor- 

 mations is to proceed at first speedily and to attain a point of equi- 

 librium beyond which further progress is relatively very slow. This 

 point of equilibrium in the case of starch acted upon by malt extract 

 under the conditions in which Brown and Heron experimented was 

 reached when the mixed products possessed a specific rotation 

 ( a ) j = 162*6, and a reducing power K = 49'3, properties which cor- 

 respond to a mixture composed of 



Maltose 80'9 

 Dextrin 191, 

 and which might be expressed by the reaction 



10 C 12 H 20 10 + 8 H 2 = 8 C 12 H 22 O n + 2 C 12 H 20 10 



Starch Maltose Dextrin 



Lea has however shewn that if conditions resembling those which 

 presumedly exist in the alimentary canal be realized, viz. if the 

 solution of starch be not too concentrated, if the diastatic ferment be 

 active and the sugar formed removed, there is no such limit to the 

 transformation of starch as indicated by the above equation so 

 that conversion into sugar tends to be complete. 



Maltose, for which the terms amyline or starch- 



of maltose. sugar have also been proposed, crystallises from water 



or alcohol in white crusts composed of fine needles. It 



is very soluble in water, but much less so in alcohol. It is isomeric 



with cane sugar, but its crystals possess one atom of water of crystal - 



100 C. 



lucose reduces Fehling's 

 solution. 



lisation (C J2 H 22 U + H 2 0), which is expelled at 

 Maltose is dextro-rotatory and like gluc 



1 Sheridan Lea, 'A Comparative Study of Artificial and Natural Digestion.' 

 Journal of Physiology, Vol. xi. (1890, p. 227 et seq.). 



