370 Locke 



lever, which has to follow negative changes of volume merely by virtue of 

 its own weight and that of the air-chamber cover to which it is attached. 

 The recorder is therefore, unlike Brodie's bellows, incapable of following 

 very rapid changes in volume such as those producible by a tuning-fork 

 acting on a tambour. Its rapidity of action is, however, sufficient for all 

 ordinary physiological experimental work. It gives, for instance, excellent 

 results as an oncograph. 



The calibration curve of the recorder resembles that of Brodie's. 

 Starting from zero, i.e. with the air-chamber emptied by the weight of 

 the cover and writing-lever, successive uniform increases of volume (of 

 05 c.c. or 1 c.c.) produce successively greater movements of the lever for 

 the first 10°-15° of its upward rotation, after which equal increases of 

 volume produce sensibly et^ual movements of the writing- lever till 

 distension is approached. For most purposes it may be assumed that only 

 the middle portion of its range would be employed, in which no special 

 reduction of the excursions obtained to correct relative values is necessary. 



The volume-recorder here described was shown to the Physio- 

 logical Society on 20th January 1906. 



III. A Perfusion Stopcock. 



A stopcock was described by me four years ago,^ which among other 

 possibilities permitted practically as rapid a change from one perfusion- 

 fluid to another as is possible with an ordinary three-way tap, whilst 

 wiving at will a bye-pass to the jfluid not being perfused, so that any ill- 

 effect when turned on of its previous stagnation may be avoided. To 

 accomplish this two separate three-way " keys " in one barrel were 

 employed. The tap here described effects it with one key only, which is a 

 considerable simplification. 



The construction, as may be seen from fig. 8, is based on the well-known 

 Greiner and Friedrichs three-way tap, both the barrel and key of which 

 are modified. 



To the middle of the bp-rrel at right angles to the other three tubes is 

 attached a fourth tube D, to act as a bye-pass to either A or B, conveying 

 the two perfusion-fluids employed. The tube C, connected with the per- 

 fused organ, is functionally prolonged upwards and forwards for a quarter 

 of the circumference of the barrel by a channel blown out from it and 

 bulging out its front. 



Two trans.verse channels, each occupying a little more than half the 

 circumference of the key, are ground out of its surface in the planes of A 

 and B on opposite sides of it, so that the outer ends of the two parallel 

 oblique key-borings open at the middle points of these channels, which 

 form functional continuations of them. 



1 F. S. Locke, Proc. of the Physiol. Soc, March 19, 1904 ; Journal of Physiology, 

 xxxi., p. xii. 



