170 THE CIRCULATION 



cian of the condition of the circulation in four particulars 

 its rate, regularity, force, and fulness ; and nearly every 

 disease modifies in some respect the condition of the pulse. 

 A very ingenious instrument, known as the sphygmograph, or 

 pulse-writer, has recently been invented, by the aid of which 

 the pulse is made to write upon paper its own signature, or 

 rather to sketch its own profile. This instrument shows with 

 great accuracy the difference between the pulses of health and 

 those of disease. In Fig. 42 is traced the form of the pulse in 

 health, which should be read from left to right. That part of 

 the trace which is nearly perpendicular coincides with the 

 contraction of the ventricles, while the wavy portion marks 

 their dilatation. (Bead Note 12.) 



39. The Veins. The vessels by which the blood returns to 

 the heart are called veins. They, like the arteries, contain 

 three coats, inner, middle, and exterior. They are largely, 

 however, composed of condensed connective tissue, and contain 

 a much smaller quantity of muscular and elastic fibres. They 

 are consequently more flaccid and compressible than the 

 arteries, and are less elastic and contractile. At first they 

 are extremely small; but uniting together as they advance, 

 they constantly increase in size, reminding us of the way in 

 which the fine rootlets of the plant join together to form the 

 large roots, or of the rills and rivulets that flow together to 

 form the large streams and rivers. In structure, the veins 

 resemble the arteries, but their walls are comparatively in- 

 elastic. They are more numerous and communicate with 

 each other freely in their course by means of interlacing 

 branches. 



ninety-six times ; of a tapir, forty -four times ; of a horse, forty times ; of 

 a wolf, forty-five times ; of a fox, forty-three times ; of a bear, thirty- 

 eight times ; of a monkey, forty-eight times ; of an eagle, one hundred 

 and* sixty times. It was impossible to determine the beatings of the 

 elephant's pulse. A butterfly, however, it was discovered, experienced 

 sixty heart pulsations in a minute." 



88. The pulse as an index f Of what does it inform the physician ? Instrument for 

 recording pulsation ? 



89. What are the veins 2 o do they form ? What do they resemble ? 



