264 ANNUAL OF SCIENTIFIC DISCOVERY. 



MECHANISM EMPLOYED IN THE CIRCULATION OF THE BLOOD. 



In a recent lecture on the above subject before the Royal Institution, 

 London, Professor Marshall attributed the heart's rhythmical movements 

 to the alternate contraction and expansion of the auricles and ventri- 

 cles, its slight rotary movement, its two peculiar sounds, one long and 

 soft, due to the closure of large valve 5 * ; the other, sharp and abrupt, 

 due to the closing of the small, semilunar valves. The pujse was at- 

 tributed to the pulsations or waves of the mass of blood, caused by 

 the elongation and distension of the elastic walls of the arteries, and 

 said to be simultaneous with, but distinct from, the onward flow of the 

 blood. By means of an ingeniously-contrived apparatus, these pulsa- 

 tions have been measured in a number ofcimmals. They are found to 

 increase as the size of the animal diminishes, e. <7-,the average pulse 

 of a horse is fifty-five beats in a second ; of a man, seventy-two ; of a 

 dog, ninety-six ; of a rabbit, two hundred and twenty ; of a squirrel, 

 three hundred. Yet it is found that, whatever be the size of the ani- 

 mal, the number of beats required to complete the circulation through 

 the whole body averages twenty-seven, and the proportion of the 

 weight of the blood to that of the whole averages one twelfth. While 

 in health AVQ are perfectly unconscious of the existence of the compli- 

 cated mechanism employed in the circulation of our blood ; this -ia 

 due to the position of the heart, and its relation to the nervous system. 



INFLUENCE OF EFFORTS OF INSPIRATION ON THE HEART. 



Dr. Brown-Sequard has communicated to the Royal Society his 

 " Experimental Researches on the Influence of Efforts of Inspiration 

 on the Movements of the Heart." 



A very interesting fact, of which many circumstances have been 

 carefully investigated by Professor Donders and Dr. S. W. Mitchell, 

 has received a wrong explanation from those physiologists. This fact 

 consists in a diminution of either the strength or the frequency of the 

 beatings of the heart when an energetic effort at breathing is made 

 and maintained for half a minute or a little more. Professor Donders 

 thinks that this influence of inspiration on the heart is due to a me- 

 chanical agency of the dilated lungs on this organ. Dr. Brown-Se- 

 quard continues, - 



It is admitted that the state of the lungs has a great influence on the 

 heart, but the principal cause of the diminution in the movements of 

 this organ is very different from what has been supposed by Professor 

 Donders, by Professor J. Mtiller, and others. It is known that when 

 the medulla oblongata or the par vagum is excited (either by galvan- 

 ism, as the Brothers Weber have discovered, or by other means, such 

 as a mere compression, or a sudden wound, as I have found), the 

 heart's beatings diminish or cease entirely. Whether this stoppage be 

 due to the cause I have attributed it to or not is indifferent to my 

 present object. What is important is that in these cases an irritation 

 on the origin of the par vagum acts through it on the heart to diminish 

 or to destroy its action. I thought that it would be interesting to de- 

 cide, if, at the time that there is an effort at inspiration, there is not 

 also an influence of the medulla oUongata on the par vagum, more or 

 less similar to that which exists when we galvanize or otherwise irritate 



