612 THE CHEMISTRY OF THE URINE. 



this was milk-sugar. Only lately, however, has it been recognised that 

 laetosuria is an almost constant phenomenon during lactation. Even 

 when the conditions are altogether favourable and normal, it is seldom 

 that the sugar is not present in the urine at some portion of the period. 

 When any interruption to the natural removal of the milk occurs, the 

 amount may be very considerable. 



The phenomenon is easily understood when it is remembered that 

 the lactose excreted into the blood from the mammary gland does not 

 come under the normal influence of the liver. Eecent researches, 

 indeed, indicate that milk-sugar cannot in any case act as a precursor 

 of glycogen, until it has been inverted. When lactose is taken by the 

 mouth, this inversion occurs before or during absorption from the bowel. 



The complete identification of lactose in the urine is difficult, unless it be 

 first isolated by processes too lengthy to be described here. But if the urine 

 exhibit the following characters, the presence of lactose is established almost 

 without the possibility of doubt. It should reduce copper and bismuth solu- 

 tion ; but, with the fermentation test, it should give negative results for the 

 first twenty-four hours of the experiment, and it should give no definite crystal- 

 line precipitate with the phenylhydrazine test when this is directly applied. 1 

 On the other hand, after boiling with 5 per cent, sulphuric acid for a short time, 

 the urine should, if first neutralised with ammonia, give the phenylhydrazine 

 test readily; crystals of dextrosazone should be thus obtained, and, with 

 proper precautions, galactosazone crystals may be also distinguished. Although 

 the lactose is converted by the mineral acid into dextrose and galactose, a 

 fermentation is not always to be obtained after treatment, as the large amount 

 of sulphate, which is present after neutralising the acid, interferes with the 

 growth of the yeast. If the reducing power of the urine be estimated, this 

 should be found increased after boiling with mineral acid, but unaffected by 

 boiling with citric acid. 



(d) Pentoses Xylose, arabinose (C 5 H 10 O fi ). Ebstein, 2 Salkowski, 3 and 

 others have observed the presence of 5 -carbon sugars in the urine. 

 They are generally, when present, derived from the food, and then pro- 

 bably arise from certain fruits, especially cherries and plums, which 

 contain either pentoses or a precursor of these sugars, the so-called 

 " fruit gum." The pentoses are apparently assimilable with difficulty. 

 Under exceptional circumstances, it seems possible that they may 

 arise in the organism, as the result of disordered metabolism. It has 

 been found that a certain proteid, derived from the pancreas, yields 

 pentoses when boiled with acids, and some such substance may be the 

 source of pentosuria. 



The pentoses give a red coloration when treated with strong hydrochloric 

 acid in the presence of phloroglucin (Tollens' reaction). Glycuronic acid, 

 however, behaves similarly. They reduce copper solutions, and yield an 

 osazone after somewhat prolonged warming with phenylhydrazine, but they 

 do not ferment. 



(e) Isomaltose. When the mixture of carbohydrates obtained from 

 normal urine by precipitation with benzoylchloride is fermented with 

 yeast, so that all the dextrose present is destroyed, there remain small 



1 Lactosazone does not crystallise readily, except from pure solutions of the sugar. 



2 Firchow's Archiv, 1892, Bd. cxxix. S* 40] ; cxxxii. S; 368. 



3 Centralbl. f. d, med. Wissenscli., Berlin, 1893, S. 193; Berl. klin. Wclmschr., 

 1895, No, 17. 



