PHYSIOLOGICAL CHEMISTRY 457 



Schiff's Reagent. 1 grm. finely powdered rosaniline hydrochloride and 100 c.c. 

 water are placed in a small bottle with a closely fitting stopper. Sulphur dioxide 

 is passed in from a syphon, till the dye just dissolves to a yellow solution, when 

 the liquid is very nearly saturated with the gas. The reagent loses sulphur 

 dioxide rather readily, so that it must be kept closely stoppered, and must 

 be resaturated occasionally with sulphur dioxide. The formaldehyde standard 

 with 0*5 c.c. of the reagent and 5 c.c. dilute formaldehyde solution (2 mg. 

 formaldehyde) made up to 100 c.c. with water should be of such a depth of 

 colour, that by the colorimeter 1'3 to 1'7 cm. is equivalent in colour to 0*7 cm. 



yrrf: potassium permanganate. 



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The method can be applied to urine either directly, or after rendering alkaline 

 with sodium carbonate and evaporating on the water bath, but not more than 

 40 c.c. of urine of specific gravity 1020 should be employed for one distillation in 

 either case, as with more urine frothing is liable to occur. 



Glycuronic acid forms a source of error, but may be removed by means of basic 

 lead acetate. For this purpose 25 to 200 c.c. urine are measured into a 500 c.c. 

 graduated flask. Slight excess of basic lead acetate solution, 10 c.c. strong ammonia 

 and water to make 500 c.c. are added. The contents of the flask are well mixed, 

 allowed to stand for a short time and filtered through a dry filter into a dry flask. 

 A measured volume of the filtrate (350 c.c. or less) is evaporated in a dish on the 

 water bath, sodium carbonate solution being added to keep the liquid alkaline. 

 The residue in the dish is then washed into the distillation flask with 40 c.c. water 

 and 45 c.c. sulphuric acid and treated as above. This treatment causes a small 

 loss of lactic acid, so that only about 50 per cent, of minute quantities of lactic 

 acid added to urine are recovered. When the quantity of lactic acid is consider- 

 able, however, the loss is negligible. 



In order to apply the method to blood the following preliminary procedure is 

 necessary. The blood, of which 20 c.c. is usually quite sufficient, is diluted about 

 five times, heated to boiling in order to coagulate the proteins, and filtered. The 

 coagulum is very thoroughly washed with boiling, faintly acidulated water. The 

 total liquid thus obtained is rendered alkaline with sodium carbonate, evaporated 

 and employed for the determination. 



Lactic acid has been found in all tissues, but the amount present 

 depends on the condition of the tissue and on the method employed for 

 killing it. Muscle, for instance, forms lactic acid during the onset of 

 rigor. Lactic acid appears to be a normal constituent of blood, but its 

 amount is variable. In the venous blood of man at rest its amount 

 varies between 10 mg. and 20 mg. per 100 c.c., but the arterial blood 

 of animals, particularly rabbits, shows higher values up to 100 mg. per 

 100 c.c. 



By the ether extraction method lactic acid has never been found in 

 normal urine, but this does not preclude its presence in small quantity. 

 By the distillation method, however, lactic acid is always present in 

 urine, amounting in man on an ordinary diet to about 4 mg. per hour 

 during the day and 2 mg. at night when determined directly, or to 

 about half this quantity when determined after lead acetate treatment. 



