GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 167 



addition to this we find small amounts of creatinin and of various xanthin 

 bodies, as xanthin, hypoxanthin, carnin, carnic acid, and sometimes traces of 

 urea, uric acid, taurin, and glycocoll. The chemical nature of these bodies 

 need not be considered here. Physiologically they may be regarded as waste 

 products which result from the partial oxidation of the proteids of muscle 

 during the katabolic processes which are continually occurring even in the 

 resting muscle protoplasm. Monari has shown that the amount of matin 

 and creatinin is increased by the wear and tear of muscular work, although 

 the proteids of the well-fed muscle probably supply but little of the energy 

 which is set free. 



The non-nitrogenous constituents of muscle are fats, glycogen, inosit, dex- 

 trose, and lactic acid. 



Fats are usually found in intermuscular connective tissue, and there is 

 some within the normal fibre. It is doubtful whether fat plays a direct part 

 in the ordinary metabolic processes involved in the action of muscles, although 

 it is probable that if more available sources of energy are lacking it may, like 

 the proteids, be altered and employed. Bogdanow l states that the fat which 

 is within the muscle-fibre is of different constitution from that between the 

 fibres ; the extracts contain more free fatty acid. He further found that the 

 fat within the fibre is used up during the work of the muscle, and is con- 

 tinually renewed from the blood. If a muscle of a frog be removed from 

 the circulation and tetanized, it stains much less with osrnic acid than one 

 with its circulation unimpaired; while a muscle which is curarized, and so 

 does no work, if it has a good blood-supply, stains much darker than ordinary 

 muscle. Under pathological conditions large amounts of fat may be found 

 inside the sarcolemma ; in phosphorus-poisoning the degenerated muscle-pro- 

 toplasm may be replaced by fat in the form of fine globules. 



Glycogen is found in very variable amounts in different muscles. The work 

 of many observers has shown that it is here, as in the liver, a store of carbo- 

 hydrate material, and is employed by the muscle, either directly or after con- 

 version into some other body, as a source of energy. The quantity, which is 

 rarely more than ^ per cent., lessens rapidly during starvation and muscle 

 work. 



When it is required, it is changed to dextrose, and is finally oxidized to 

 C0 2 and H..O. If the action of the muscle is prevented by the cutting of 

 the nerve or of the tendon, the glycogen is found to accumulate. 



Sugar is found in muscles in small quantities only ; nevertheless it probably 

 plays an important part, for ( 'hauveau and Kaufmann, by studying the levator 

 labii superioris of the horse, found that the muscles take sugar from the blood. 

 and that they take more during action than rest. The sugar which the mus- 

 cle takes during rest is for the most part stored as glycogen.-' Although sugar 

 is considered a source of muscle-energy, the exact way in which it is employed 

 is doubtful. 



1 Arehiv fur Anatomie vmd Physiologic, 1897, 8 1 l'.'. 



2 Qmiptt'x rrnrfus rfc la Sorictr (If Biologic, 1886, civ. 



