144 APPLIED PHYSIOLOGY 



arrest of haemorrhage. Some drugs also e.g., ergot 

 cause a direct contraction of the muscle fibres, whilst 

 others e.g., the nitrites cause them to relax. 



In addition to their muscular elements, the arteries 

 possess an outer fibrous coat which is purely protective, 

 and an inner endothelial lining which is designed to 

 lessen friction. Underneath this is a delicate layer of 

 connective tissue which, although it does not bulk largely 

 under the microscope, is of great importance in disease, 

 for in it many of the pathological processes which affect 

 the arteries have their starting-point. 



The Arterial Pulse. 



The pulse is of such extreme clinical importance that 

 a thorough knowledge of its mode of production and 

 physiological characters is essential to the physician. 

 It is necessary at the outset to clear the mind of two 

 misconceptions about the pulse, which are still very 

 prevalent : (1) It is not due to the transference of a 

 wave of blood along an artery, but to the transference 

 of a wave of pressure; (2) it is not due to a change in 

 size or distension of an artery, but to a change in its 

 shape. 



The blood discharged from the left ventricle during 

 its systole is accommodated in the large vessels imme- 

 diately beyond the heart, and merely raises the pressure 

 throughout the smaller arteries without actually dis- 

 tending them, the rise of pressure being transmitted 

 along the columns of blood contained in the arteries 

 in the form of the wave called the ' pulse.' To suppose, 



