238 PHYSIOLOGICAL PHYSICS. [Chap. xxi. 



moist. The effect of heat or cold can be stupied by 

 surrounding the vessel h by an outer vessel con- 

 taining hot or cold water, and a thermometer in 

 the salt solution will give the temperature. The 

 little projecting wire c on the canule is for at 

 taching a copper wire to be carried to one of the 

 binding screws of a key. Another wire from the 

 other binding screw dips into the salt solution sur- 

 rounding the heart by passing down the tube of h. 

 A little mercury in the botuom of this vessel will make 

 the connection better. By this means shocks may be 

 sent to the heart, and tracings of the -effect of electric 

 currents obtained. Into the second burette may be 

 placed a blood solution, similar to that in the first, but 

 having in addition a small quantity of ether, chloroform, 

 or other substance. By turning the cock the proper 

 way any required quantity of the drugged blood may 

 be sent to the heart and its effects recorded. 



The projection c of the canule (Fig. 114) is for the 

 attachment of a wire from an induction coil. The 

 second wire from the coil is passed into the bottom of 

 the vessel h in which the heart is placed. A little 

 mercury is poured into the vessel, and into it the wire 

 dips. The heart is thus in the circuit of the coil, and 

 effects of shocks of electricity may be studied. 



Lauder Brimton has shown a simple way of 

 demonstrating the effect of heat and poisons on the frog 

 heart. He cuts out the heart, places it on a copper 

 plate, and lays o\ar it a light lever of straw or some 

 such material. The lever indicates the heart's pulsa- 

 tions. On heating the plate, by means of a spirit 

 lamp, the heart's pulsations are quickened, on cooling 

 with ice they are slowed. 



Marey has devised a pair of light forceps for 

 grasping the heart in situ, the thorax being opened. 

 Only one limb of the forceps can move ; and a lever 

 in connection writes on a blackened surface. 



