INTUOD.J PHYSIOLOGY TO MEDICINE. 29 



nerve could not be the seat of a very painful disease, for it is itself, 

 in a very great degree, devoid of sensibility. It need hardly be 

 added, that the operation is discarded. 



The dangerous disease, to which many children have fallen 

 victims, laryngismus stridulus or crowing inspiration, although ad- 

 mirably described by practical physicians, was never properly un- 

 derstood until the functions of the laryngeal nerves were clearly 

 ascertained, and until it had been shown that spasmodic actions 

 may be excited by irritation of a remote part, or through a stimu- 

 lus reflected from the nervous centre. It is now known, that this 

 disease has not its seat in the larynx, where those spasms occur 

 which excite so much alarm for the fate of the little patient ; but 

 that it is an irritation of a distant part, which derives its nerves 

 from the same region of the cerebro-spinal centres within the 

 larynx, that the afferent nerves of that part convey the irritation 

 to the centre, whence it is reflected by certain efferent nerves to 

 the muscles of the larynx. 



The accurate diagnosis of diseases of the heart rests entirely 

 upon a correct knowledge of the physiology of that organ. This 

 improvement in medicine may be said to date from the time of 

 Harvey, for he was the first who clearly expounded the mechanism 

 of the central organ of the circulation. But the application of 

 auscultation to the exploration of the sounds developed in its 

 action, and the correct interpretation of those sounds in health by 

 the experiments and observations of the last few years, have almost 

 completely removed whatever difficulties stood in the way of the 

 detection of cardiac maladies. 



We are not less indebted to the illustrious Englishman, who dis- 

 covered the circulation of the blood, for having paved the way to a 

 rational treatment of aneurismal and wounded arteries by the 

 modern operation of placing a ligature between the heart and the 

 seat of the disease or injury. " The active mind of John Hunter," 

 says Mr. Hodgson, " guided by a deep insight into the powers of 

 the animal oscoiiomy, substituted for a dangerous and unscientific 

 operation, an improvement founded upon a knowledge of those laws 

 which influence the circulating fluids and absorbent system; and 

 few of his brilliant discoveries have contributed more essentially to 

 the benefit of mankind." 



In investigating the functions of the human body, the physiolo- 

 gist cannot do better than follow the instructions laid down by 

 Haller in the preface to his invaluable work, " Elementa Physio- 

 logiae Corporis Humani." 



