CARBOHYDRATES. 39 



Milk-sugar, also called lactose or lactobiose, occurs similarly in nature, 

 and was described as long ago as 1615 by Fabricio Bartoletti in the 

 " Encyclopaedia dogmatica," and described in 1700 by Testi and in 1715 

 by Vallisneri as a newly-discovered medicine. Milk-sugar is found in vary- 

 ing amounts in the milk of all mammals. During confinement it is often, 

 found in small quantities in the urine. 1 Similarly in calving it has been 

 detected in the urine for several days before and after the birth. Again 

 after weaning, sugar is wont to pass off through the kidneys. Recently, 

 Porcher 2 has carefully studied the origin of the lactose in milk. He found 

 that extirpation of the breast-glands of milch-goats and cows soon caused 

 a marked increase in the amount of sugar in the blood, while, at the same 

 time, glucose appeared in the urine. These experiments make it seem 

 very probable that the milk-sugar is first formed in the breast, and appar- 

 ently from glucose alone, and not out of the glucose and galactose in the 

 food 



Milk-sugar has never been found in the vegetable kingdom. 3 On 

 being subjected to hydrolysis it breaks up into one molecule of glucose 

 and one of galactose. By oxidizing it with nitric acid, mucic acid, 

 COOH . (CHOH) 4 . COOH, is formed. 



Maltose, also called malt-sugar, maltobiose, ptyalose, and cerealose, 

 occupies a quite different position from the above two disaccharides. It 

 is a cleavage product of starch, and in fact an intermediary product which 

 usually is immediately hydrolyzed further as fast as it is formed. It is 

 true that small amounts of maltose are met with now and then in plant 

 organisms, and it is quite possible that it is here also a transitory product 

 in the metabolism of carbohydrates. Recent investigations make it seem 

 probable that maltose is also found as a glucoside in the vegetable kingdom. 



In animal organs (liver, blood, etc.) maltose has been repeatedly found, 

 although always in small amounts; and furthermore, in many cases the 

 methods of identification have not been entirely satisfactory. The most 

 important manner of formation is by the action of a ferment upon starch. 



As long ago as 1785 Irvine, and in 1815 KirchhoftV observed that extract 

 of malt was capable of breaking down starch. The sugar formed was 

 recognized first by Dubrunfaut 5 in 1822. The active principle in malt, 

 the so-called diastase, was first isolated by Payen and Persoz. 6 Starch 



1 Cf. Franz Hofmeister: Z. physiol. Chem. 1, 101 (1877-78). P. Kaltenbach: ibid. 

 2, 360 (1878-79). F. A. Lemaire: ibid. 21, 442 (1895-96). 



2 Ch. Porcher: Compt. rend. 141, 73 and 467 (1905). 



3 Bouchardat [Compt. rend. 73, 462 (1871)] claimed to have found milk-sugar in the 

 ripe fruit of achras sapota, but this has not been confirmed. 



4 Schweigger's J. 15, 389. 



5 Ann. chim. phys. 3, 21 and 178. 



6 Ibid. 2, 53, 56, 73, and 337. 



