452 TEXT-BOOK OF PHYSIOLOGY. 



and active. The muscle is therefore said to possess or exhibit a glyco-gen- 

 etic function. During the periods of prolonged activity of the muscles the 

 percentage of glycogen rapidly diminishes, a fact that leads to the inference 

 that it is the source in large part of the energy expended by the muscle. 

 During the period of rest the percentage of glycogen rapidly increases un- 

 until the normal is regained. 



The metabolism of the carbohydrates or the manner in which they are 

 stored, transformed and finally oxidized is a subject about which there is 

 much obscurity and uncertainty. Some light is thrown on the problem by a 

 consideration of the pathologic state known as 



Diabetes. Diabetes is a chronic disease characterized by the appear- 

 ance of sugar in the urine in variable amounts. Under normal circumstances 

 all the sugar consumed as food undergoes oxidation to carbon dioxid and 

 water, none appearing in the urine except the merest trace. In some dis- 

 ordered states of nutrition this oxidation is imperfect or entirely lacking. 

 The sugar therefore accumulates in the blood after which it is eliminated in 

 the urine in large, though variable amounts, a condition which may endure 

 for months or years though eventually leading to the death of the individual. 

 The pathologic condition underlying this incomplete oxidation is imper- 

 fectly understood and has usually been associated with derangements of the 

 glycogenic function of the liver, though doubtless derangements of other 

 organic functions will produce the same condition. At the present time it 

 is believed that the persistent excretion of sugar by the kidneys depends on 

 several causes: (i) An ineffectual abstraction and storage of sugar due to 

 some impairment in the activity of the liver cells ; (2) an incomplete oxida- 

 tion in the muscles by reason of the absence of the necessary enzymes; (3) a 

 cleavage of the protein constituents of the tissues, in consequence of some 

 profound alteration in the nutritive process, whereby their glucose radicals 

 are liberated in unusual amounts. 



The physiologic mechanism by which the normal metabolism of the carbo- 

 hydrates is regulated is obscure and but imperfectly known. That it is com- 

 plex in character is shown by the phenomena which follow not only puncture 

 of the medulla, and other injuries to and disturbances of the nerve system, but 

 also removal of the pancreas and the administration of various toxic agents. 



Nerve influences, whether the result of injuries to the nerve system or of 

 various pathologic states occasionally apparently precede and cause the 

 diabetic state, though the manner in which they do so is practically unknown. 

 Some light is thrown on the process by a consideration of the facts 

 detailed in a previous paragraph relating to the influence of the nerve system 

 in the production and storage of glycogen in the liver. It is quite possible 

 that nerve impulses abnormally developed may lead to an incomplete 

 storage of glycogen by the liver-cells, the result of an imperfect nutrition or 

 a deranged circulation. 



Removal of the pancreas from the body of a dog or other animal is in a 

 few days followed by a rise in the percentage of sugar in the blood and its 

 elimination by the kidneys. In a short time acetone, aceto-acetic and 

 /?-oxybutyric acids make their appearance, attended by the usual symptoms 

 characteristic of glycosuria in man. Death usually occurs at the end of 

 three or four weeks. The quantity of sugar excreted and the gravity of the 



