800 PHYSIOLOGY 



similar consumption of glucose occurs in the isolated contracting mammalian 

 heart when fed with Einger's fluid containing a small trace of glucose. A 

 heart, fed with blood and performing a normal amount of work, may use 

 about 4 mg. sugar per gramme of heart muscle per hour. That the question 

 of utilisation of sugar by the tissues is highly complex is shown by a study 

 of the conditions under which sugar may appear in the urine. We learn 

 thereby to appreciate to some extent the significance of carbohydrates both 

 as sources of energy and as foods for the tissues, though we are still a long way 

 from unravelling all the changes which the sugar must undergo in the cell 

 before it appears once again in the oxidised products, carbon dioxide and 

 water. 



GLYCOSURIA 



Normal urine always contains a small proportion of sugar, about 1 part 

 per 1000, i.e. about the same as the blood itself. For the detection of these 

 small traces of sugar in the urine special methods are necessary. The term 

 glycosuria is not employed unless sugar appears in quantities large enough 

 to give a reaction with Fehling's solution or with the phenylhydrazine test. 

 Such a condition may easily be brought about by the injection of sugar 

 subcutaneously or intravenously. It is then found that any trace of the di- 

 saccharides, cane sugar or lactose, introduced in the circulation, is excreted 

 in the urine. A rather larger quantity of maltose may be injected slowly 

 without appearing in the urine, since the blood- serum contains a ferment 

 maltase, which converts the maltose into glucose. Glucose, fructose, man- 

 nose, or galactose, if introduced slowly into the circulation, are stored up 

 as glycogen in the liver. If, however, the percentage of sugar in the blood 

 rises above 2 -parts per 1000, the sugar (generally glucose) appears in the urine. 

 When this condition of hyperglycsemia (excess of sugar in the blood) is set up, 

 the concentration of the sugar in the urine no longer corresponds to that in 

 the blood. If the blood contains, e.g. 4 parts per 1000, the urine may contain 

 from 2 to 7 per cent, of sugar. Up to a certain point, then, blood- sugar is 

 kept back by the kidneys as a necessary food material for the tissues. Any 

 excess above the normal apparently acts as a foreign substance and is 

 excreted by the kidneys in a concentration much greater than that in which 

 it exists in the blood-serum. 



(1) ALIMENTARY GLYCOSURIA. A state of hyperglycasmia may be 

 induced by the administration of abnormally large quantities of glucose 

 by the alimentary canal. The amount has to exceed in a healthy individual 

 100 grm. in order that it shall appear in the urine. In certain individuals the 

 power of assimilating glucose may be deficient so that an alimentary glyco- 

 suria may be caused by. any over-indulgence in carbohydrate food. In the 

 healthy person it is hardly possible to produce glycosuria by the administra- 

 tion of starchy foods, since the liver can store up the excess of glucose as fast 

 as it is produced from the starch by digestion and absorbed into the blood 

 stream. 



(2) DIABETIC PUNCTURE. It was shown by Claude Bernard that 

 puncture of the floor of the fourth ventricle in rabbits is often followed 



