CIRCULATION OF THE BLOOD. 547 



the inhibitory ganglion and the apparatus intermediate between the ganglion, I, 

 and the motor ganglion. On the other hand, muscarine slows the heart or stops 

 it in diastole, similar to irritation of the vagus, while its effects are not interfered 

 with by either the previous or subsequent injection of nicotine : therefore, mus- 

 carine must act on some apparatus more central than that affected by nicotine, 

 and as the effects are gradually developed, it is supposed to act by irritating the 

 ganglion, I. Again, we have seen that muscarine will have no effect after the in- 

 jection of atropine, and that atropine will cause a heart stopped by muscarine to 

 recommence beating ; therefore, atropine acts on a more central apparatus than 

 muscarine: in other words, on the apparatus intermediate between I and M. The 

 effects of atropine may be removed by physostygma and is antagonistic to 

 nicotine. These points are valuable in determining the antidotal effects of 

 poisons. 



The action of the accelerator apparatus has not been so thoroughly well 

 worked up, but the action of poisons, as of veratrine, renders it necessary to 

 assume a similar arrangement. 



There is one more point in the action of these cardiac ganglia ; that 

 is, the influence of heat and cold on the heart. 



The simplest method of studying the action of heat on the cardiac 

 pulse is that of Lauder-Brunton (Fig. 230). His arrangement consists 

 of a plate of glass about three inches by four inches, at one end of 

 which a cork is cemented projecting about half an inch beyond the edge 



7 



FIG. 230. LAUDER-BRUNTON'S ARRANGEMENT FOR STUDYING THE EFFECT 

 OF HEAT AND COLD ON THE HEART OF THE FROG. 



of the glass plate. To this is fastened a long, light lever freely moving 

 on a pivot, and projecting about one and one-half inches beyond one end 

 of the plate and about four inches beyond the other end ; the lever is 

 counterpoised by fastening a small pair of forceps on the short end of 

 the lever ; by altering the angle of the forceps, the lever can be balanced 

 to a nicety. A frog's heart may be placed on the plate close up to the 

 pivot and lying so that the lever is lifted at each pulsation of the ven- 

 tricle, the lever being balanced so as to make slight pressure by altering 

 the position of the pair of forceps. If the glass plate is placed on some 

 pounded ice the heart will beat gradually more and more slowly, until at 

 length it will come to rest in diastole, thus indicating irritation of some 

 portion of, the inhibitory apparatus. If the plate be removed from the 

 ice, the heart will commence again, and by gradually heating it over a 

 spirit-lamp the heart will pulsate faster and faster, the extent of the 

 contractions increasing up to 20 C., until at length it will stand at rest 

 in what is called u heat-tetanus ; " if, however, the temperature is lowered 

 the heart will again commence to beat, but if the temperature is raised 



