Mr. J. Douglas on the Source of Muscular Force. 273 



In the determination of each curve I use a delicately adjusted 

 rheostat or scale of resistances in the circuit of x, giving it 

 varying values corresponding to the equal divisions of the en- 

 graved scale, and constructing the curve according to the position 

 which it is found necessary to give to the point s' in order to 

 arrive at the magnetic balance. With each instrument it would 

 be possible to have two values of R — one expressed in mercury 

 and the other in B.A. units ; and in order to measure at pleasure 

 in either of these units, it would only be necessary to insert the 

 one or other between the terminal screws for R. 



The instrument has been found to be very convenient for the 

 measurement of the wire resistances of overland lines, or for the 

 reading of resistance thermometers; it reduces the operation 

 to the observation of the zero position of a needle, and the 

 reading upon a graduated scale, which can be performed by a 

 person of ordinary intelligence without experience in electrical 

 measurement. In accuracy and range it fully equals the bridge 

 method, while as regards portability and cheapness of apparatus 

 the advantages are decidedly in its favour. 



XXXV. On the Source of Muscular Force. By John Douglas, 



East-India Government Telegraph Department*. 



THE attempts hitherto made to settle the question of the 

 source or sources of muscular energy have consisted in 

 calculating the quantity of muscle, the component nitrogen of 

 which would equal either the nitrogen ingested or excreted during 

 the performance of certain measured external work. 



The consideration of the ingesta appears to promise the most 

 reliable results if the nitrogen be reduced in quantity until just 

 sufficient to support the body in health. In considering ingesta, 

 it may be known for certain that all the effective nitrogen is in- 

 cluded in the calculation ; in considering excreta there is no such 

 certainty. The data furnished by ingesta may be collected over 

 a longer time than those furnished by excreta, the latter being 

 obtained only by continued expenditure of time and labour on 

 the part of the observer and subject or subjects under observation ; 

 and that generality so desirable in physiological inquiries is almost, 

 if not quite, unattainable in the consideration of excreta, whereas, 

 as shown below, it is easily attainable in considering ingesta. 



The only source of the nitrogen of the muscles is the food, it 

 being generally admitted that none is absorbed under ordinary 

 circumstances by the lungs and skin. Observers agree on this 

 point, although difference of opinion exists as to its evolution by 

 those organs. 



* Communicated by the Author. 



