THE CIRCULATORY SYSTEM 171 



found. Some of these pass through the walls of the blood 

 capillaries with the plasma which forms the lymph, but 

 all along the course of the lymphatics are small -glands 

 made of networks of connective tissue which hold in their 

 meshes large numbers of small white corpuscles packed 

 sicle by side as closely as possible. The lymph, flowing 

 into these glands on one side and from them on the other 

 side, carries along with it some of these corpuscles and 

 thus keeps the blood supplied. These lymphatic glands, 

 or similar tissues in the body, are the source of the white 

 corpuscles of the blood. 



237. Hygiene of the Circulation. In perfect health the 

 blood circulates rapidly, because the heart beats strongly, 

 the muscular tone of arteries and veins is such as to pro- 

 mote the flow, the blood is purified in the lungs by an 

 abundant supply of pure air, plenty of fresh material is 

 supplied to it from suitable, well-digested food, the nerv- 

 ous centers are quickly responsive to their natural stimuli, 

 and furnish the needful impulse to the numerous parts of 

 the circulatory apparatus. 



The blood cannot circulate freely unless the whole body 

 is so loosely clothed that there is no pressure upon any of 

 the blood vessels, no restriction of the breathing capacity, 

 no interference with the normal action of the stomach, 

 liver, and intestines. There must be exercise of all the 

 muscles, sleep sufficient to keep the nervous system in 

 good condition, and activity of the excretory organs. 

 The last is promoted by exercise, frequent bathing, 

 friction of the skin, and the wearing of woolen under- 

 garments. 



238. Effects of Alcohol upon the Blood and the Circulation. 

 The first effect of dilute alcohol taken into the stomach 

 appears to be to make the heart beat faster and with 



