3 48 Messrs. G. A. Buckmaster and J. A. Gardner. [Aug. 19, 



Description of Plethysmograph. 



The instrument consisted of a rectangular glass box, fitting into a groove 

 channelled in a thick slate slab forming the floor of the chamber. The box 

 was of such a size as to comfortably hold a cat. In order to make it airtight, 

 the groove was filled up with a stiff mixture of vaseline and beeswax. The 

 dimensions of the box were as follows: length 67 cm., breadth 32 cm., 

 depth 17 cm. Four holes were bored through the slate bed near the corners 

 of the box. These were fitted with rubber corks, through which passed glass 

 tubes of wide bore. The two holes at one end were connected with one 

 another by a Chauveau's valve apparatus. Through a third hole, a wide tube 

 led to a recording gasometer, made of aluminium, similar to that used by 

 Haldane and Priestley* The drum of the gasometer was 8 cm. high, and 

 6 - 2 cm. diameter. The gasometer, carrying a light adjustable recording lever, 

 rose and fell in a bath of paraffin oil, which appeared to possess advantages 

 over water. The inertia of this part of the apparatus was inappreciable. 

 The fourth hole was connected with a bottle into which a burette fitted for 

 purposes of graduation, and this was carried out and tested in the manner 

 described in the paper just quoted. 



The dimensions of the gasometer given were found to be most suitable for 

 cats. In investigating respiratory ventilation, it is obviously important to 

 avoid as far as possible breathing through long tubes and systems of valves. 

 To minimise these disadvantages, the mixture of chloroform and air was passed 

 through the Chauveau's valves at a slight positive pressure, and the percentage 

 composition kept constant by the use of Waller's chloroform balance.f The 

 animal actually respired through a cannula connecting the trachea with the 

 central tube of the Chauveau's valve apparatus. This tube was as wide and 

 short as possible, the length in every case being less than the distance of the 

 tracheal opening from the mouth. It was found that expansion of air, owing 

 to rise of temperature, caused no trouble, as during the time taken to seal 

 up the box the temperature had become constant. 



The general mode of procedure was as follows: — The animal was anaes- 

 thetised with nitrous oxide, and a cannula quickly placed in the trachea. 

 The cannula was fitted on to the Chauveau valves, the glass box placed on 

 the slate slab, and the whole chamber made airtight. When the animal 

 recovered from nitrous oxide, chloroform of known percentage was adminis- 

 tered by Waller's balance. In those experiments where a knowledge of 

 the gas-content of the blood was required, the animal received 3 c.c. of strong 



* ' Journ. Physiol.,' 1905, vol. 32, p. 486. 

 t ' Journ. Physiol.,' Feb. 22, 1908, vol. 37. 



