THE PHYSIOLOGY OF MUSCULAR WORK 229 



pulse wave, and in some cases extends the information which may 

 be obtained by the hand alone. By palpation it is possible for the 

 practised hand to gauge the pressure of the blood, but for accurate 

 determinations the Riva Rocci sphygmometer is generally used. 



The circulation can be studied in several ways ; by inspection 

 the colour of the skin affords a guide to the flow of blood in the 

 peripheral parts, and the information so obtained may be checked 

 and extended by the use of flat bulb thermometers with which 

 the temperature of the surface of the skin can be determined. 

 The plethysmograph will measure the changes in the volume of 

 a limb which are due to alterations in the supply of blood, and 

 modifications of the sphygmometer, which indicate the pressures 

 at which the arterioles, capillaries, and veins are blanched, will 

 measure the pressure of the blood in those vessels. 



This is not the place for details of the practical use l of the 

 various instruments which have been mentioned, but it will not 

 be amiss to point out that the simplest are the best. The striving 

 for exact results by the use of complicated pieces of apparatus 

 often defeats the aim ; it is far better to multiply simple obser- 

 vations under different conditions than to spend much time and 

 labour in obtaining a record with a complicated instrument, how- 

 ever exact it may appear to be. For this warning there are two 

 strong reasons. The effects of muscular exercises upon the heart 

 and circulation quickly disappear when a healthy man takes rest ; 

 the recovery begins at once, and during the seconds and minutes 

 spent in the adjustment of apparatus great changes may occur. 

 The second reason is a practical one. The medical man engaged 

 in a busy practice has not the time, means, or experience necessary 

 for the successful use of many scientific instruments, and it is far 

 better that he should rely upon his own powers of observation by 

 sight and touch. 



In the study of the effects of muscular exercise upon the heart 

 and circulation it is always necessary to know the normal con- 

 ditions of the subject during rest. The personal variations in 

 different individuals are so great that data are deprived of a great 

 part of their value unless they combine the results of observations 

 both before and after exercise. 



It is desirable that a writer should give the results of investi- 

 gations conducted by himself or in conjunction with others. The 



1 See "Practical Physiology," by Beddard, Edkins, Hill, Macleod, and 

 Pembrey, second edition, 1905. 



