612 THE CHEMISTRY OF THE URINE. 
this was milk-sugar. Only lately, however, has it been recognised that 
lactosuria 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 he 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 5 ). — Ebstein, 2 Salkowski, 3 and 
others have observed the presence of 5 -carl ion 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. 
" Virchow's Archiv, 1892, Bd. exxix. S* 401 ; exxxii. S. 368. 
3 Centralbl. f. d. med. Wissensch., Berlin, 1893, S. 193; Berl. klin. IFchnschr., 
1895, No. 17. 
