TISSUES OF THE BODY. 299 



When the question is started, Where are we to suppose these mineral 

 constituents to exist, whether in the fibre or its nutritive fluid 1 the fol- 

 lowing fact may be borne in mind, that the proportion of salts soluble in 

 water which are present in flesh is very considerable. The former amount, 

 according to Clievreul, to 81, and to Keller, to 82 '2 per cent of the whole 

 ash, while the quantity of phosphate of calcium is stated to be 5 - 77, 

 and that of magnesian phosphate 12 '2 3 per cent. Of course a 

 larger proportion of potash compounds must occur in the fluid of 

 muscle than in the fibre itself, whereas the latter is richer in phosphatic 

 earths. 



Living muscle contains, further, carbonic acid and oxygen gases. The 

 latter is absorbed by it so long as its vitality exists, while carbonic acid 

 is generated within it as a product of decomposition, whether blood be 

 conveyed through it or no. The amount, moreover, of the latter increases 

 with the use of the muscle, which appears to be one of the most import- 

 ant sources of this ultimate product of mutation in the body. 



Smooth muscles, with the contractile substance of their cell body and 

 their nuclei, manifest less complication than those formed of striated 

 fibres, but appear on account of their smaller bulk less suitable objects 

 for chemical investigation. Their composition appears, moreover, to 

 be the same as that of the striped tissue. Syntonin has naturally 

 been obtained from them also (Lehmann). Further, in their juices 

 albuminous substances have been found kreatin, hypoxanthin, lactic, 

 acetic, formic, and butyric acids. Here also the potash combinations 

 predominate. 



REMARKS. 1. Bibra states the proportion of water in the human muscle to be 

 only 72-74 percent, as opposed to the usual figures, 77-78. 2. Among the fishes 

 we find the muscular tissue of the plagiostoma to contain enormous quantities of urea 

 (Staedeler and Frerichs in Erdvianris Journal, Bd. 73, p. 48, and Bd. 76. p. 58). 3. 

 The same observers found, further, a substance very similar to inosite in the muscles of 

 the plagiostoma ; this is named ", 



171. 



In regard to the many physiological and physical properties of the 

 tissue, a few points only heed be touched on here. 



Quiescent living muscle displays a high degree of extensibility, return- 

 ing almost completely to its original length as soon as the extending 

 force is suspended ; it has slight, but very perfect elasticity. The active 

 fibre is still more extensible, i.e., its elasticity has undergone diminution. 

 The dead muscle fibre possesses much less capability for being extended, 

 and return to its original length does not take place. 



The living structure possesses electromotor properties, and presents 

 the so-called " muscular stream," in the study of which Du Bois- 

 Reymond has lately done so much. We cannot here enter upon its 

 differences during quiescence and activity of the muscle. The latter 

 ceases to possess electromotor properties so soon as its vitality is at an 

 end. 



The most important property, however, of the living muscle fibre 

 (striped and smooth) is, that it contracts on stimulation of the motor 

 nerves terminating in it, decreasing in length, and enlarging it in a trans- 

 verse direction. The nature of this peculiar property inherent in muscle 

 whether it be itself capable of being excited, or only through the medium 

 of the nerves which end in it has been now for many years the subject 

 of physiological controversy. 



