VIII. MUSCLES AJS'D SERVES. 953 



is then fastened by sealing-wax to one end of the lever, and to the other end 

 of the straw a round piece of white paper, cut to the size of a shilling or half- 

 crown, according to convenience, is also fixed by a drop of sealing-wax. The 

 pin, which acts as a pivot, should be just sufficiently beyond the edge of the 

 plate to allow the lever to move freely, and the lever itself should lie flat upon 

 the plate. Its weight, too, increased as it is by the straw and paper flag, 

 would now be too great for the heart to lift, and so it must be counterpoised. 

 This is readily done by clasping a pair of bull-dog forceps on the other end. 

 By altering the position of the forceps the weight of the lever can be regulated 

 with great nicety. If the forceps are drawn back as at c, Fig. 1, the flag is 

 more than counterbalanced, and does not rest on the heart at all, while the 

 position a brings the centre of gravity of the forceps in front of the pivot, and 

 increases the pressure of the lever on the heart. The isolated frog's heart is 

 laid under the lever near the pivot, and as it beats the lever oscillates up- 



wards and downwards. If the tin plate be now laid on some pounded ice, 

 the pulsations will become slower and slower, and if the room be not too 

 warm the heart may stand completely still in diastole. On removing the plate 

 from the ice the pulsations of the heart become quicker. If a spirit lamp be 

 now held at some distance below it, the heartbeats quicker and quicker as the 

 heat increases, until at last it stands still in heat tetanus. On again cooling 

 it by the ice its pulsations recommence. At first they are quick, but they 

 gradually become slower and slower. On again applying the spirit lamp 

 they become quicker, and by raising the temperature sufficiently the heat 

 tetanus is converted into heat rigor. Then no application of cold has the 

 slightest effect in restoring pulsation. 



Not only the effects of heat and cold, but the effect of separating the 

 venous sinus or the auricles from the ventricle can readily be shown with 

 this apparatus, as well as the action of various poisons. The best for the 

 purpose of class demonstration is muscaria. A drop of saline solution con- 

 taining a little of the alkaloid being placed on the heart, it ceases to beat 

 entirely. If a drop of atropia solution be now added, the beats recommence. 

 The exhibitor has seen them do so on one occasion after they had entirely 

 ceased for four hours. When used for demonstrating the action of poisons 

 the wooden lever should be covered with sealing-wax, so as to allow every 

 particle of the poison to be washed off it, and thus prevent any portion from 

 being left behind and interfering with a future experiment. By attaching a 

 small point to the end of the straw in place of the paper flag, tracings may be 

 taken upon smoked paper fixed on a revolving cylinder. 



3798. Hosenthal's Rotating Myographion, constructed by 

 Th. Edelmann, of Munich. P r ^f. Rosenthal, Erlangen. 



This myographion, lately constructed by the exhibitor, and not hitherto 

 described, consists of a large glass plate, which is swiftly rotated round a hori- 

 zontal axis, by a weight. As soon as the desired velocity is attained, the glass 

 plate is slightly displaced parallel to itself in the direction of its axis. It makes 



