Page:The Principles and Practice of Medicine.djvu/45

Rh The blood of anaemic persons is thin and watery, and mani- festly deficient in red corpuscules. In some cases the proportion has been found to be as low as 30 parts in 1 ,000. The decrease in the proportion of fibrin is by no means equally great, and consequently the blood coagulates with a firm clot, frequently having a buffy coat.

The important bearing of anemia in diseases of tropical climates can scarcely be over-estimated. Not only is it the chief predisposing cause of these diseases, but it exercises a marked influence upon the phenomena they present, and upon the action of the remedies which are employed for their cure.

in the circulation of the blood are either general or local. General derangement, connected with or dependent upon disease of the heart, will form a part of Special Pathology.

Pulse. We become aware of general derangement of the cir- culation by examining the pulse. The pulse is the sensation felt when one or more fingers are placed over an artery during the con- traction of the heart. It is caused by temporary increase in the size and length of the vessel. In arteries near the heart it is synchronous with the contraction of the ventricles or systole of the heart ; in arteries at a distance it is little later, but the difference is scarcely appreciable by ordinary observation.

The information afforded by the pulse has reference to num- ber, size, density, regularity, and nature of the beat.

Number. The number of times the pulse can be felt in a minute varies at different periods of life, in different persons, and in the same person at different times. At birth it beats about 140 times in the minute. From birth to moderate old age it diminishes in frequency, but undergoes a slight increase during decrepitude. The following may be taken as averages :