BY DR. BURDON-S ANDERSON. 2 



diastolic interval, and thus, indirectly, to render the individual 

 contractions of the heart feeble and less effectual. How they 

 act, and what is their anatomical and physiological relation 

 either to the ganglion cells, or to the vagus of which they are 

 the antagonists, it is not at present possible to explain. As 

 has been already stated, the heart of the frog does not receive 

 any accelerator nerves. From the following experiment, how- 

 ever, it appears that the vagus nerves in that animal contain 

 accelerator fibres. To demonstrate this, the animal must be 

 placed under the influence of nicotin, which alkaloid, as lately 

 shown by Schmiedeberg, possesses the power of paralyzing the 

 terminations of the inhibitory fibres contained in the trunk of 

 the vagus, without affecting the intrinsic inhibitory ganglia of 

 the heart. If in a frog, into which about a thirtieth of a grain 

 of nicotin has been injected, one vagus nerve is excited, the 

 excitation, instead of arresting the heart in diastole, or dimin- 

 ishing its frequenc}', accelerates its contractions. And if, 

 instead of injecting the solution under the skin, the heart is 

 prepared after Dr. Coats's method, supplied with serum con- 

 taining nicotin, and connected with the kymograph, and 

 observed before, during and after excitation of the vagus, 

 tracings are obtained which show that the frequency of the 

 heart-beats is increased sixty per cent.; that the acceleration 

 commences about four seconds after the opening of the key, 

 and lasts about a minute and a half after the cessation of the 

 excitation; and that it is due to shortening, or rather annull- 

 ing, of the diastole, each systole following immediately on the 

 close of the preceding one (see fig. 2*4). 



82. Demonstration of the Functions of the Depres- 

 sor Nerve. In the rabbit as well as in the cat, a cardiac 

 branch separates itself from the vagus at the level of the thy- 

 roid cartilage, high in the neck, and ends in the inferior cervical 

 ganglion. In the rabbit, the nerve commonly originates in 

 two roots, one of which springs from the superior laryngeal, 

 the other from the vagus 'tself, near the point at which the 

 laryngeal leaves it; but very often it is derived exclusively 

 from the superior laryngeal. In its course towards the inferior 

 cervical ganglion, it is close to the carotid arteiy, and still 

 closer to the sympathetic trunk, from which it is distinguished 

 by its smaller size and whiter aspect. From the ganglion the 

 fibres of the depressor are continued downwards, forming the 

 two most internal of the filaments which in the rabbit pass be- 

 tween it and the heart. They can be traced to the connective 

 tissue between the origin of the aorta and pulmonary artery. 

 The depressor contains centripetal fibres, the function of which 

 is to diminish the activity of the vasomotor centre, and thereby 

 diminish the arterial pressure. 



A rabbit is chloralized ; one carotid is connected with the 



