200 



THE CIRCULATION OF THE BLOOD AND LYMPH 



groove, just sufficient to lay bare the wires on the upper side, is made 

 in it, and the nerve is laid in this groove.) 



Experiments 7, n (i) and n (2) will be rendered more exact by 

 connecting a second electro-magnetic signal with a Pohl's commutator 

 without cross-wires (Fig. 94), in such a way that the circuit is inter- 

 rupted at the instant when stimulation begins. 



12. The Action of Inorganic Salts on Heart- Muscle. Expose and 

 remove the heart of a tortoise or turtle (p. 196). Cut off the apical two- 

 thirds of the ventricle by an incision parallel to the auriculo-ventricular 

 groove. By a second parallel cut remove a ring of tissue 2 or 3 milli- 

 metres wide from the upper end of this portion of the ventricle. Divide 

 the ring at opposite ends of a diameter, so as to form two strips. Tie 

 a fine silk thread to each end of one strip. Attach one of the threads 

 to the short limb of a glass rod bent at right angles, so that it can be 

 immersed at will in a beaker. The other end of the rod is fixed in a 

 holder sliding on a stand. Attach the second thread to the short arm 



Fig- ?3- Arrangement of Induction Machine for Tetanus. B, battery; K, simple 

 key ; P, primary coil ; S, secondary coil ; A, C, binding screws to be connected 

 with battery 46r single shocks; F, G, binding screws for tetanizing current; N, 

 Neef's hammery D, short-circuiting key in secondary; E, electrodes. D and E 

 are drawn to a much larger scale than the rest of the figure. 



of a counterpoised lever arranged to write on a slowly-moving drum. 

 If the strip is still beating, wait till the contractions have ceased ; then 



(1) Immerse the strip in a beaker filled with o'y per cent, solution of 

 sodium chloride. After a time it begins to beat rhythmically. The 

 contractions become rapidly stronger, and then after a while diminish, 

 and gradually cease. The tone or tonus of the strip is diminished by 

 the solution. 



(2) Arrange the other strip in the same way, and immerse it in a 

 solution of calcium chloride (about I per cent.) isotonic with the sodium 

 chloride solution used in (i). If the strip is contracting, the contrac- 

 tions will cease. Rhythmical contractions will not appear as in the 

 sodium chloride solution. The tone of the strip may be increased. 



(3) Remove most of the calcium chloride solution from the beaker, 

 and fill it up with 0-7 per cent, sodium chloride solution. The rhythmi- 

 cal contractions will appear after a longer or shorter latent period, and 

 will be stronger and last for a longer time than in the sodium chloride 

 solution alone. 



(4) Immerse a fresh strip in a solution containing sodium chloride 



