Recovery from this form of fatigue takes a much longer time than the preceding. The individual is too tired to sleep, the night is troubled by disturbed dreams, there is a soreness and stiffness of the muscles and joints which remain for some days. There may be an actual rise in temperature, and the urine passed has a high specific gravity, with sometimes even albumin. If, now, this overwork is continued over prolonged periods of time, without allowing sufficient time for the necessary recuperation, there follows a slow and profound exhaustion, which is much more difficult to overcome. In this condition the temperature becomes subnormal, the weight decreases, the skin and muscles become flabby, and the skin is pale, the eyes are dull and listless, and the individual is without ambition to rouse herself from her lethargy. During a contraction each muscle-cell shortens and thickens, giving off some of its substance into the lymph-space which surrounds it, and absorbing food, consisting of carbohydrates and oxygen, from the surrounding plasma. Exercise improves nutrition by the rhythmic, automatic massage caused by the contraction and relaxation of the muscles on the vessels which they contain, while warmth favors the elimination of waste matter. It has been proved by Hawk, of the University of Pennsylvania, in his experiments on the blood-count of an athlete in training, that various forms of active muscular exercise produce an average increase of 16.8 per cent. in the number of red corpuscles. When exercise is long-continued, the rate of increase lessens, and, further, the number may be decreased in greatly prolonged violent exercise. The explanation of this is that a large number of cells lie inactive in various tissues of the body until they are brought into the circulation by muscular exercise. [Illustration: PLATE III Senegalese woman. (From Stratz, after Dr. Rykens, in Shufeldt’s “Studies of the Human Form.”)] Athletic training has been called “mainly heart training.” Exercises of endurance do not require supreme efforts, but they do accelerate the action of the heart and lungs, and the aggregate of work done is very much greater than in exercises of strength, but the exercise must be sufficiently active to provide for the free circulation of lymph, which is carried on mainly through the massage of muscular contraction. If a walk be so listless that there is not sufficient movement of the muscles to overcome the pernicious influence of gravity acting on the column of blood contained in the veins of the abdomen, thighs, and legs, the vessel-walls may become permanently overstretched and varicose. The exercise must be sufficiently active for the muscular contractions to empty the lymph-spaces and hasten the circulation. It usually raises the general bodily, as well as the local, temperature of the parts, and so facilitates the removal of the waste-products.