Action of the Heart. 517 



cial exertion of any part, that part must receive an extra or unusual 

 supply of blood. As the ancient doctors stated it, Wherever there is 

 stimulation, thither flows the blood. "Ubi irritatio, ibi affluxus. " Dur- 

 ing the activity of an organ the amount of blood in it may be increased 

 30 per cent. , or even 47 per cent ; and generally the amount of blood in 

 any part or organ varies to correspond with its condition of activity. 

 ( Landois. ) The extra supply is obtained by an increase in the rate of 

 pulsation, and this increase appears to be due to two causes. One cause 

 is, that as soon as a part receives an extra stimulation, a part of the 

 stimulation is communicated by the nervous system to the heart, caus- 

 ing extra exertion on its part, accompanied by a larger supply of blood 

 to it by way of the coronary arteries. The other cause is mechanical, 

 and results from relief of the pressure of the blood in the arteries. 

 Whenever a particular part is active, the arterial blood in that place is 

 more rapidly consumed, and the materials thus abstracted from the ar- 

 teries, or an equivalent amount in the shape of waste matter, is thrown 

 into the veins. This, by relieving the pressure against which the heart 

 works, allows it to work faster. The whole arrangement is very much 

 like a system of city water works, where the pressure is maintained in 

 the pipes by the pumps. The pipes are the arteries, and the thousands 

 of outlet cocks used by consumers, are the fine capillaries or hair-like 

 tubes into which the arteries subdivide in the tissues of the body ; the 

 sewers are the veins. The strokes of the pumps fluctuate with the de- 

 mand for water. In the night they are slow, faster in the day-time, 

 fastest if an extraordinary demand arise, as in case of fire. So, the 

 circulation of the blood and the pulsation of the very pump-like heart 

 are slow at night, when, in sleep, the activity of the body is reduced to 

 a minimum. For the ordinary duties of the day the pulsation is 

 increased, while an extraordinary exertion may almost double it. A 

 middle aged man may, in a few minutes, by violent exercise, raise the 

 pulse from 70 to 110, and the respiration from 18 to 28 per minute. 

 The ordinary pulse steadily declines in rapidity from infancy to old age. 

 It is most rapid during the period of the relatively most rapid growth 

 and greatest activity. It is stated by some authorities to be 140 per 

 minute at birth, at the age of one year, 120, at three years, 100, at 

 twenty years, 85, in the middle of life, 70, and in old age, 50 to 60. 



As mentioned above, the nervous ganglions in the heart are connected 

 with the general nervous system of the body, by means of which con- 

 nection the condition of the body has more or less influence on the ac- 

 tion of the heart. The chief of these connections are a branch of the 

 pneumogastric or vagus nerve, and branches from the three cervical gan- 

 glia and the first thoracic ganglia of the great sympathetic nerve. The 

 first of these is called the inhi 'l't<>r>j nerve of the heart, because when it 



