Contributions to Physiological Technique 369 



seat, is made to lie. The ends of this have been previously fused in the flame, 

 so that they only form apertures nicely admitting a sewing-needle of No. 9 

 size. Such a needle, preferably one longer than ordinary and known techni- 

 cally as a " Straw," is now thrust through the rubber collar on one side, 

 through the length of the glass tube and out through the rubber collar on 

 the other side, taking care not to injure the condom, the projection out- 

 wards of the rubber collar by the ends of the glass tube making this easy. 

 Its sharp end is now cut off so that only a few millimetres project on 

 either side. 



The magnalium-plate, shaped as shown in fig. 6, the hinges and w^riting- 

 lever attached to it being formed by cutting and bending, is now fitted to 

 the needle-axis, two beads on each side, or a bead and glass spangles as in 

 fig. 6, minimising side-lash and friction. 



If preferred the plate can now be fixed to the summit of the condom by 

 a touch of rubber solution. I have not myself found this to be any advan- 

 tage. The merely resting plate immediately forms the condom into the 

 folds natural to it, which if not disturbed remain permanently the same. 

 If the condom has been fitted carefully and symmetrically, preferably with 

 its summit projecting a little forward and its seam, if it have one, in 

 the middle line, the folds assumed by it are surprisingly regular and 

 symmetrical. 



For actual use the recorder is best fixed by means of its glass tube in a 

 clamp in the somewhat oblique position shown in fig. 6. 



Many variations in the details of construction can of course be made. 

 Instead of rubber, cork or suberit shives can be used to build the 

 recorders on. But both of these substances are so leaky that they 

 must be completely and fairly thickly covered externally with 

 Prout's glue or some such substance, the edges of the condom being 

 embedded in this. The cover and its hinge can be made in different 

 ways of different materials. Cardboard can be used instead of 

 metal, hinged by a strip of soft silk to another piece of cardboard 

 slipped under the rubber collar, the rubber stopper being cut flat 

 on one side to receive this. The needle-axis, if used, can be simply 

 made by thrusting the needle through the thickened seam of the 

 rubber collar when this is made of " inner tube " turned inside )ut, 

 but this method ia by no means so lasting as the one described 

 above. 



It might be thought that the use of a thin distensible rubber air- 

 chamber was not permissible in a volume-recorder, but if care be taken 

 that the cover moves easily on its axis and that there be no excessive 

 friction of the writing-point, no rise of pressure occurs in the air-chamber 

 sufficient to introduce error in ordinary volumetric work. The absence of 

 any real elasticity of form in the limp air-chamber wall prevents, of course, 

 any suction applied to the air-chamber acting directly upon the recording 



