CIRCULATION. 141 



the blood would be a very serious error, easily avoided by bearing in mind 

 the causes of the pulse-wave as already given. 



Investigation by the Finger. — The feeling of the pulse has beeD a valu- 

 able and constantly used means of diagnosis since ancient times. Indeed, the 

 ancient medicine attached to it more importance than does the practice of 

 to-day. But it is still advisable to warn the beginner that he may not look 

 to the pulse for "pathognomonic" information ; that is to say, he may not 

 expect to diagnosticate a disease solely by touching an artery of the patient 

 under examination. The pulse is most commonly felt in the radial artery, 

 which is convenient, superficial, and well supported against an examining 

 finger by the underlying bone. Many other arteries, however, may be util- 

 ized. 



Frequency and Regularity. — The most conspicuous qualities of the pulse 

 are frequency and regularity. Usually these can be appreciated not merely by 

 a physician but by any intelligent person. The physiological variations in 

 the frequency of the heart's beats have been referred to already (p. 121). In 

 an intermittent pulse the rhythm is usually regular, but, at longer or shorter 

 intervals, the ventricle omits a systole, and therefore, the pulse omits an up- 

 stroke. Either intermittence or irregularity of the cardiac beats may be 

 caused by transient disorder as well as by serious disease. 



Tension. — When unusual force is required in order to extinguish the pulse 

 by compressing the artery against the bone, the arterial wall, and hence the 

 pulse, is said to possess high tension, or the pulse is called incompressible, or 

 hard. Conversely, the pulse is said to be of low tension, compressible, or soft, 

 when its obliteration is unusually easy. A very hard pulse is sometimes called 

 "wiry;" a very soft one, "gaseous." High tension, hardness, incompressibil- 

 ity, obviously are directly indicative of a high blood-pressure in the artery ; 

 and the converse qualities of a low pressure. It follows from what has gone 

 before that the causes of changes in the arterial pressure, and hence in the 

 tension, may be found in changes either in the heart's action, or in the periph- 

 eral resistance, or, as is very common, in both. An instrument called a 

 sphygmomanometer 1 or sphygmometer is sometimes applied to the skin over 

 the artery, in order to obtain a better measurement of its hardness or softness, 

 and hence of the blood-pressure within it, than the finger can make. Such 

 instruments are not free from sources of error. 



Size. — When the artery is unusually increased in calibre at each up-stroke 

 of the pulse, the pulse is said to be large. When, at the up-stroke, the calibre 

 changes but little, the pulse is said to be small. A very large pulse is some- 

 times called "bounding;" a very -mall one, " thready." Largeness of the 

 pulse must be distinguished carefully from largeness of the artery. The for- 

 mer phrase means that the fluctuating pari of the arterial pressure is large 

 in proportion to the mean pressure. But if the mean pressure be great 

 while the fluctuating part of the pressure i- relatively small, the artery, even 

 at the end of the down-stroke, will be of large calibre, while the pulse will 



be small. 



' From r < >v) u6i , pulse. 



