1883.] Mr. W. North. On the Discharge of Nitrogen. 11 



a vacuum the phenomena observed by Savart do not take place, all 

 kinds of powder collecting at the nodes. In the investigation of 

 this, as of the other problems, the motion is supposed to take place 

 in two dimensions. 



It is probable that the colour phenomena observed by Sedley Taylor* 

 on liquid films under the action of sonorous vibrations are to be referred 

 to the operation of the aerial vortices here investigated. In a 

 memoir on the colours of the soap-bubble, f Brewster has described 

 the peculiar arrangements of colour accompanied by whirling motions 

 caused by the impact of a gentle current of air. In Mr. Taylor's 

 experiments the film probably divides itself into vibrating- sections, 

 associated with which will be aerial vortices reacting laterally upon 

 the film. 



The third problem relates to the air- currents observed by Dvorak 

 in a Kundt's tube, to which is apparently due the formation of the 

 dust figures. In this case we are obliged to take into account the 

 compressibility of the fluid. 



VII. " The Influence of Bodily Labour upon the Discharge of 

 Nitrogen." By \V. North, B.A., F.C.S. Communicated 

 by Professor J. S. Burdon Sanderson, F.luS. Received 

 October 29, 1883. 



(Abstract.) 



The scope of this inquiry has been strictly limited to one question, 

 viz., that of the influence of labour in modifying the normal relation 

 between food and excreta. No attempt has been made to investigate 

 the mode in which nitrogenous products come into existence in the 

 organism. 



The researches immediately bearing on the subject of this paper are 

 those of Dr. Parkes (" Proc. Roy. Soc," vols. 16 and 21), and those 

 of Dr. Austin Flint, made on the pedestrian Weston (" New York 

 Med. Journal," June, 1871). Dr. Parkes found that bodily exercise 

 caused a slight increase in the nitrogen discharge during or imme- 

 diately after labour. The increase was, however, so inconsiderable that 

 it may well be questioned whether it could not be accounted for as 

 dependent on the more perfect absorption of food ; for although the 

 diet of the soldiers experimented upon was carefully regulated, and 

 the nitrogen it contained determined by analysis, with the result that 

 before work the quantity of nitrogen taken in considerably exceeded 

 the quantity discharged, the two became practically equal during the 

 work period. Consequently if the whole period of observation is 



* " Proc. Roy. Soc," 187S. f " Edinburgh Transactions," 1866-67. 



f 



