CHEMICAL BASIS OF THE ANIMAL BODY. 1223 



phenyl-hydrazine upon it in presence of acetic acid. It crystal- 

 lizes readily in minute yellow needles and is characterized by 

 being (unlike phenyl-glucosazone) soluble in about 75 parts of 

 boiling water, and still more soluble in hot alcohol. Its melt- 

 ing-point, 206°, is practically the same as that of phenyl-glucosa- 

 zone. 



The researches referred to above (p. 1190) shewed that 

 whereas pancreatic juice rapidly converts starch-paste into 

 maltose and a little dextrose, an extract of the mucous mem- 

 brane of the small intestine or the tissue itself, while acting but 

 feebly on starch-paste, rapidly converts maltose into dextrose. 

 It was hence surmised that maltose would be found to be a 

 non-assimilable sugar, requiring like cane-sugar to be converted 

 into the simpler dextrose before absorption. More recent 

 experiments have confirmed this view, for it has been found 

 that if maltose be injected into the blood-vessels it is largely 

 excreted in an unaltered form in the urine. The converting 

 action of extracts of the intestinal mucous membrane is strik- 

 ingly less than that of the tissue itself ; from this it may per- 

 haps be inferred that the change into dextrose takes place rather 

 during than previous to absorption. This fact corresponds 

 closely to the well-known views as to the changes which pep- 

 tones similarly undergo during their passage through the walls 

 of the intestine into the neighbouring blood-vessels (see § 250). 



3. Lactose (Milk-sugar). C 12 H 22 O n -l-H 2 0. 



It is found characteristically and solely in milk, in quantities 

 varying with the class of animal and at different times with the 

 same animal. The percentage is relatively high in human milk. 

 It is also said to occur in the urine of lying-in women and 

 sucklings. 



Preparation. The casein is precipitated from diluted milk by the 

 addition of acetic acid. The filtrate from this is boiled to coagulate 

 the remaining proteids which are then removed by filtration. This 

 final filtrate is then concentrated and on prolonged standing yields 

 crusts of milk-sugar which are purified by recrystallization from hot 

 water. 



It yields, when pure, hard colourless crystals, belonging to 

 the rhombic system (four-sided prisms). It is less soluble in 

 water than dextrose, requiring for solution six times its weight 

 of cold, but only two parts of boiling, water ; it is entirely 

 insoluble in alcohol and in ether. It is fully precipitated from 

 its solutions by the addition of basic lead acetate and ammonia. 



Solutions of many metallic salts are readily reduced by boil- 

 ing with lactose, but the reducing power is less than that of 

 dextrose. Thus 1 c.c. of Fehling's fluid, which is reduced by 



