102 



ACTION OF FLUIDS ON THE HEART. 



[Methods. The action of fluids upon the excised frog's heart has been rendered 

 possible by the invention of the "frog-manometer" of Ludwig. The apparatus 

 has been improved by Ludwig's pupils, and already numerous important results 

 have been obtained. The apparatus, Fig. 32 consists of (1.) a double-way 

 cannula, c, which is tied into the heart, h-, (2.) a manometer, m, connected with e, 

 and registering the movements of its mercury on a revolving cylinder, cyl ; (3.) 

 two Mariotte's flasks, a and &, which are connected with the other limb of the 

 cannula. Either a or b can be placed in communication with the interior of the 

 heart by means of the stop-cock, s. The fluid in one graduated tube may be 

 poisoned, and the other not; d is a glass .vessel for fluid, in which the heart 

 pulsates, e and e' are electrodes, e is inserted into the fluid in d, e' is attached to 

 the german silver cannula which is shown in Fig. 32a. 



Fig. 32. 



Scheme of a frog-manometer a, 6, 

 Mariotte's flasks for the nutrient 

 fluids; s, stop-cock; c, cannula; 

 m, manometer ; 7i, heart ; d, glass 

 cup for h; e, e', electrodes; cyl, 

 revolving cylinder. 



Fig. 32a. 



Double- way or perfu- 

 sion cannula (nat. 

 size) for a frog's 

 heart c, for fixing 

 an electrode ; d, the 

 heart is tied over the 

 flanges, preventing 

 it from slipping out ; 

 e, section of d. 



In the tonometer of Roy (Fig. 33) the ventricle, h, or the whole heart, is placed 

 in an air-tight chamber, o, filled with oil, or with oil and normal saline solution. 

 As before, a "perfusion" cannula is tied into the heart. A piston, p, works up 

 and down in a cylinder, and is adjusted by means of a thin flexible animal mem- 

 brane, such as is used by perfumers. Attached to the piston by means of a thread 

 is a writing lever, I, which records the variations of pressure within the 

 chamber, o. When the ventricle contracts, it becomes smaller, diminishes 

 the pressure within o, and hence the piston and lever rise ; conversely, when 

 the heart dilates, the lever and piston descend. Variations in the volume of 

 the ventricle may be registered, without in any way interfering with the flow 

 of fluids through it. 



Two preparations of the frog's heart have been used (1.) The "Aar," in which 

 case the cannula is introduced into the heart through the sinus venosus, and a 



