960 SEC. 18. BIOLOGY. 



3961. Gas-Chamber for electro - physiological experiments 

 particularly with living membranes. Prof. JEngelmann, Utrecht. 



The bottom of the chamber is an ebonite disc, diameter 13 cm., thickness 

 13 mm., resting on three small feet. Lid, a glass shade, height 12cm., diameter 

 11 cm., with a broad flat ground rim resting in a groove of the ebonite disc ; 

 through the perforated neck a thermometer can be introduced. 



On the bottom of the chamber 6 binding screws, each separately in elec- 

 trical connexion with corresponding binding screws on the outside of the 

 chamber. 



Inside the chamber, between the binding screws the object-support is 

 placed, an ebonite plate furnished with : 



1st. A central vertical vice to fix a horse-shoe cork frame upon which the 

 animal membrane is spread. 



2nd. On each side a glass pillar to fasten the electrodes. 



To conduct the electric currents from the preparation small tubular uon- 

 polari sable electrodes are used ; they are attached to lead wires and each 

 connected by a very thin wire with one of the screws. 



The other screws are to conduct electric currents, either to stimulate the 

 object or to warm it by galvanism. 



Two bent glass tubes, conducting through the bottom into the chamber, for 

 the entrance and outlet of gases. 



(Ouderzoekingen gedaan in het physiologisch laboratorium der Utrechtsche 

 Hoogeschool. Derde Reeks, II. 1873, p. 9, &c., PI. I.) 



3962. Isochronoscope. Prof. Dondcrs, Utrecht. 



A brass lever has at one extremity a registering spring and at the other 

 extremity a peg. On pressing the lever down with the hand, the spring re- 

 gisters the instant at which the peg, touching the mercury, closes the circuit 

 (white electrodes). At this instant, the physiological or psycho-physical 

 effects of this currrent, in all kinds of experiments of irritation, are registered 

 on the same cylinder. Underneath the lever are two electro-magnets. 

 When the current (green electrodes) passes, the lever is pulled down. 

 This current is used either to note certain periods of time, as seconds, on 

 the cylinder, or, by means of a more equal closing of the circuit, to obtain 

 greater equability of the irritating current than can be obtained by the hand. 

 The equable breaking of the circuit is then secured by means of a spring 

 under the lever. 



3963. Apparatus for the Determination of the Co- 

 efficient of Elasticity of the Living Muscles in Man. 



(Compare Mansvelt, Elasticiteit der Spieren. 1860. Diss. iuaug. 

 Utrecht, 1863.) Prof. Donders, Utrecht. 



A vertical wooden board, sliding up and down in a stand with foot, has 

 on its upper side a little sliding beam, and on its surface two recesses, which 

 are the centres of two graduated arcs. With the face directed towards the 

 profile of the board, the operator leans with the shoulder against an extremity 

 of the cross beam and softly presses the internal condyles of the humerus into 

 one of the recesses. The humerus has a vertical position ; the forearm is 

 stretched either horizontally at 0, or above or below this position, and a weight 

 suspended by a thread to a band round the wrist. On cutting this thread the 

 forearm springs up, and the number of degrees is read off. 



From different data the length of the muscle before and after the cut- 

 ting of the thread and the action of the weight may be calculated, whence 



