APPARATUS FOR PHYSIOLOGICAL USE. 237 



which rivals that of the accomplished musician, so the 

 physiologist is able to assign to each of the fine varieties 

 of the human pulse, which are appreciable to the accom- 

 plished touch of the physician, a curve of definite form 

 a curve expressive of that rapid succession of movements 

 to which the pulse owes its quality. 



The quality of the pulse has been long appreciated in medi- 

 cine, and the tactus eruditus has been long spoken of as the 

 faculty of the accomplished physician, who by feeling the 

 pulse with his finger can not only count its rate, but also 

 judge of its quality, for describing which he employs certain 

 more or less conventional terms, such as hardness, fulness, 

 sharpness, and others, all of which are of practical signi- 

 ficance. There is therefore a practical reason why it is 

 necessary not merely to study those slower variations of 

 arterial pressure which I have compared to tides, but also 

 those finer and more rapidly recurring changes on which 

 the peculiarities of the human pulse depend. Now in 

 order to illustrate this, I desire to make some experiments ; 

 and as we cannot make them on a living artery, we shall 

 use what is called in physiology a schema, i.e., a mechanical 

 apparatus so constructed as to imitate the living organ in 

 respect of some of its properties. 



Our schema consists of an elastic tube resembling, as 

 regards the thickness and elasticity of its walls, an 

 artery. At one end it is in communication with a pump, 

 at the other with a tube of outflow, of which the diameter 

 can be regulated by a screw. Such a tube represents an 

 artery in respect of several of its properties. 



One of the most important is that it converts the 

 intermittent motion with which water is injected into the 

 tube at the end next the pump into an equable or constant 

 progressive motion at the other. You see that the rate of 

 outflow is nearly constant, but not quite so, for if I allow 

 the water to flow out horizontally, the curve it describes 

 in falling is one of varying declivity. At each stroke of 

 the heart-pump it is thrown a little further out. 



To understand this equalization all we have to do is to 

 consider what happens to the motion communicated to the 

 liquid at each stroke. At the moment that the impulse 

 is given, liquid enters the tube at a rate which exceeds 

 that of the efflux. Motion consequently has disappeared. 



