August 15, 1834.] 



SCIENCE. 



133 



the tension of the belts may be readily regu- 

 lated. This form of stop-cock was arranged 

 some years ago by Dr. Bowditch, to be run 

 by the clock-work of the kymographion, and 

 has been described by him in the Journal of 

 physiology (ii. 3, p. 202). This interrupted 

 blast of air is carried Iry the pipes already 

 mentioned to an}' table where it is required. 

 The system was planned for the present needs 

 of laboratory-work, but could be readily ex- 

 tended even to other work-rooms. It has thus 

 far proved quite satisfactory, and readily 

 adaptable to the artificial respiration of dogs, 

 cats, or rabbits. 



Adjoining the respiration apparatus, the 

 sketch shows a filter-pump (0) and its simple 

 mercury-gauge (T), which can be attached to 

 the same system of piping, and used at a dis- 

 tance. This is done by connecting the rubber 

 tube Q with the pipe P. Although the sys- 

 tem was not originally planned for use with 

 negative air-pressures (the revolving stop-cock 

 not being quite tight enough for such a pur- 

 pose), it is very easy to produce a negative 

 pressure of two hundred and forty millimetres 

 (mercury) on the table in the lecture-room, or 

 on the more remote working-tables of the gen- 

 eral laboratory. 



At the other end of the room is a small 

 mercury-table (MT) . This is merely an ordi- 

 naiy table, with a raised edge, made tight 

 and thoroughly varnished. A little shelf at 

 one corner holds a bottle to catch the refuse 

 inercur}- directed to a hole in this corner by 

 a suitable shortening of the legs. A firm 

 shelf on the pilaster near by holds a small 

 meat-cutter (MC), and a press for extract- 

 ing meat-juice and the like. At the other 

 side of the mercury-table stands the large 

 digestion apparatus (DA), or constant tem- 

 perature box. This consists of two cylindrical 

 boxes of sheet-copper of different sizes, joined 

 by a rim at the top, and resting on legs made 

 of iron rods. The inner box has a diameter of 

 forty centimetres and a depth of twenty-nine 

 centimetres, the corresponding dimensions of 

 the outer casing being fifty-eight and thirt}-- 

 eight centimetres respectively. The rim has 

 two holes for corks carrying a thermometer 

 and a glass tube of the regulator. At the side 

 is a stop-cock for removing the water which 

 fills the space between the two shells. The 

 inner box is the air-chamber, and has a double- 

 walled cover packed with charcoal. An extra 

 cover has also been made, a thick wooden rim 

 canying two plates of glass, with an air-space 

 between, so that any changes going on in the 

 chamber kept at a constant temperature may 



be followed without removing the cover. The 

 apparatus stands thirty centimetres above the 

 floor, and, being covered with a layer of as- 

 bestos packing two centimetres thick, it parts 

 with its heat so slowly that a single Bunsen 

 burner suffices to keep it at a temperature of 

 60° C. The size of flame is determined by a 

 glycerine regulator. A large glass tube sus- 

 pended in the water contains the g^cerine, 

 which also fills a rubber tube communicating 

 on a shelf above with the regulator, and ending 

 in a small funnel. The glycerine, as the water 

 warms, expands, and rises into the funnel, 

 until, at the desired temperature, a stop-cock 

 is closed. After this an} T further expansion 

 forces a rubber membrane against the end of 

 the gas-pipe above, and shuts off the main gas- 

 supply to the flame, leaving only a small amount 

 regulated by another stop-cock, the ' pin-hole ' 

 of the ordinary mercury regulators. The con- 

 traction of the glycerine, on cooling, draws the 

 membrane down again, and thus increases the 

 gas-supply. This regulator has been found 

 very trustworthy ; and the temperature of the 

 air-chamber has remained quite constant for 

 weeks at a time, with only a very small flame. 

 Only temperatures from 38° to 60° C. have been 

 tested, but for these the variation has not 

 exceeded half a degree C. As the volume 

 of water to be heated is large, about sixty-four 

 litres, considerable time is required to raise the 

 temperature sufficiently ; and this is the only 

 practical objection to the apparatus. This is, 

 of course, compensated for b} T the size of the 

 air-chamber, rather over thirty-six litres. For 

 experiments calling for speed, there is a small 

 digestion apparatus at the table near the lecture- 

 room. This is merely a water-bath, with an 

 ordinary mercury regulator, and a water-supply 

 from a Mariotte's flask on the shelf at the 

 back. For lecture demonstrations of artificial 

 digestion, the laboratoiy has another piece 

 of movable apparatus of convenient size and 

 some elegance. 



Adjoining the glass case on the western wall 

 is the varnishing apparatus ( VA) . This is 

 a simple tin trough, slightly tipped at one end. 

 where a rubber pipe runs to a supply-bottle, 

 whose position on the shelves at the side deter- 

 mines the filling or emptying of the trough. 

 The smoked papers are run through the varnish, 

 and then suspended from rods, to drip into the 

 trough, and thus into the bottle. This form 

 of apparatus was originally devised by Profes- 

 sor Kronecker of Berlin. 



In the north-eastern corner of the laboratory, 

 adjoining the chemical table, stands a large and 

 convenient injection apparatus (IA) for the 



