GENERAL SYMPTOMS OF DISEASE. 31 



the left ventricle, suddenly collapses, and then as suddenly ex- 

 pands again, the second expansion being sometimes nearly equal 

 in intensity to the first. This constitutes dicrotism."^ — (Dr. 

 BuRDON Sanderson's Handbook of the S;pliygmograph, to which 

 the reader is referred for further information.) 



I have already stated that the pulse is the beating of the 

 arteries. In each pulsation as felt by the hand the arteries are 

 slightly expanded, distended, and elongated by the wave of 

 blood ; sometimes they are laterally displaced, and then return 

 to their original position, after which there is a short period of 

 rest — the interval. 



It seems probable that when the heart contracts of itself, it 

 does so gradually and peristaltically, its constituent fibres being 

 brought successively into action ; and that, in so far as the 

 movement is deprived of its automatic character by the influence 

 of stimuli acting through the spinal cord, it becomes sudden and 

 instantaneous. — (See on this point Dr. Burdon Sanderson, or Dr. 

 Bell Pettigrew's Paper on the Physiology of the Circulation, in 

 Lancet, 1872.) The influences concerned in the production of the 

 pulse are those of the heart, the arteries, and the blood. Tlie 

 lieart gives the impulse by which the expanding wave of blood 

 is carried onward, after which the artery contracts in virtue of 

 the elasticity of the yellow fibrous tissue which enters into the 

 composition of its middle coat, or by its additional muscular force. 



In health there is a nearly uniform relation between the 

 frequency of the pulse and of the respiratory movements ; the 

 proportions being, as nearly as possible, one respiratory move- 

 ment to three or four pulsations. Thus the pulse of the healthy 

 horse beats about forty times per minute ; the respirations are 

 from twelve to fifteen in the same time. In the cow the same 

 relationship does not exist, even in health, between the pulse 

 and respiratory movements ; for during rumination it may be 

 observed that the pulse is seventy to eighty a minute, and the 

 respirations not more tlian ten. Indeed the pulse of the cow in 

 a state of confinement, in so far as regards the number of its 

 beats, cannot be depended upon in the diagnosis of disease ; the 

 states of pregnancy and obesity, the effects of artificial food, and 

 of the activity of the lactiferous glands, as well as the excite- 

 ment caused by the act of rumination, generally produce such 



^ Double pulse. 



