XXX 



ox THE PRESEXT STATE OF KXOWLEDGE AS TO 

 THE STRUCTURE AND FUNCTIONS OF NERVE 



Roy. Inst. Froc, vol. ii., 1854-58,//. 432-437, Friday, May 15, 1857 



The speaker commenced by directing the attention of the audi- 

 ence to an index, connected with a little apparatus upon the table, 

 and vibrating backwards and forwards with great regularity. The 

 cause of this motion was the heart of a frog (deprived of sensation 

 though not of life) which had been carefully exposed by opening the 

 pericardium, and into whose apex the point of a needle connected 

 with the index had been thrust. Under these circumstances the 

 heart would go on beating, with perfect regularity and full force, 

 for hours ; and as every pulsation caused the index to travel through 

 a certain arc, the effect of any influences brought to bear upon the 

 heart could be made perfectly obvious to every one present. 



The frog's heart is a great hollow mass of muscle, consisting of 

 three chambers, a ventricle and two auricles, the latter being separated 

 from one another by a partition or septum. By the successive con- 

 traction of these chambers the blood is propelled in a certain direc- 

 tion ; the auricles contracting force the blood into the ventricle ; the 

 ventricle then contracting drives the blood into the aortic bulb ; and 

 it is essential to the full efficiency of the heart as a circulatory organ; 

 that all the muscular fibres of the auricles should contract together ; 

 and that all the muscular fibres of the ventricle should contract 

 together ; but that the latter should follow the former action after a 

 certain interval. 



The contractions of the muscles of the heart thus occur in a 

 definite order, and exhibit a combination towards a certain end. 

 They are rhythmical and purposive ; and it becomes a question of 



