442 FUNCTION OF MUSCULAR FIBRE. 



nary apparatus ; the former, in part, through the lungs. That these prod- 

 ucts are to be attributed to muscular waste is inferred from their in- 

 crease or diminution with increases or diminutions of muscular exertion. 

 In the voluntary fibres there is commonly a necessity for repose, during 

 which repair of the waste is taking place ; but in those organs which 

 are in ceaseless action, as the heart and diaphragm, the repair or nutri- 

 tion goes forward at an equal rate with the waste, and no period of rest 

 is required. It necessarily happens, during the destruction of this tis- 

 eo f tem er sue by t ne arterial blood, that a rise of temperature must 

 atureinmus- ensue, and such a rise has been actually observed to the 

 L0n * amount of a degree or more, notwithstanding the constant 

 tendency to the removal of the heat by the constant current of venous 

 blood flowing from the muscle. There is no necessity to attribute the 

 elevation of temperature to friction among muscular fibres, and, indeed, 

 the amount that could arise in that way must be very 'insignificant, and 

 not to be for a moment compared with that due to the oxidation. Even 

 in muscles which have been removed from the body, and made to con- 

 tract by the aid of magneto-electric currents, changes of composition may 

 be detected. 



OF THE FUNCTION OF MUSCULAR FIBRE. 



The mechanical action of muscular fibre depends, as we have seen, on 

 Nature of the shortening of the long axis of the cells of which the fibres 

 contractility. are composed. To this result the designation of contractility 

 is given, and the property by which the fibre is enabled to exhibit this 

 shortening is designated, agreeably to the metaphysical system of the old 

 physiologists, who were content to accept a word as an explanation of 

 a fact, by the term irritability ; this, as being useless, may be discarded ; 

 the former we may continue to employ. 



At one time it was supposed that the contraction of a muscular fibre 

 Contractility depends so completely upon the agency of the nervous system 

 enf on^hf" that it; mi g nt ^ e considered as the direct function thereof; but 

 nerves. a more critical examination of the circumstances of the short- 

 ening of the fibre cells shows that it possesses many features in common 

 with the same contraction of the cells of plants, which have no nervous 

 system. The influence passing along the nerve fibrils is only one out of 

 many which can cause muscular contraction. There is abundant evi- 

 dence in support of the position that contractility is the result of the 

 structure of the muscular fibre, and that it belongs to it, and is not a spe- 

 cial function of nerves. 



When muscular fibres are touched by a pointed instrument, they ex- 

 hibit contraction even after they have been detached from the body, pro- 

 vided that too long a period of time has not elapsed. If it be of the stria- 



