Dr. H. C. Wood, who has experimented largely on the subject in animals, finds the cause of heart failure in the coagulation of the myosin, which takes place under ordinary circumstances at 115° F., but at a much lower temperature when a muscle has been in great activity immediately before death. As the temperature of thermic fever frequently reaches 113°, or even higher, he easily accounts for the sudden syncope occurring during active work in a high temperature. As an example of such sudden rigor, he adduces the sudden stiffening of the bodies of some soldiers killed in battle during hot weather. Wood further shows that all the symptoms of thermic fever can be produced in the rabbit by concentrating the temperature on its head, which seems to imply a direct action on the brain and in particular on the heat producing and vaso-motor centres. This becomes the more reasonable that the temperature attained does not impair the vitality of the blood but, leaves the leucocytes possessed of their amœboid motion. He found, moreover, that if the heat were withdrawn before it has produced permanent injury to the nervous system, blood or other tissues, the convulsions and unconsciousness are immediately relieved and the animal recovers. Other conditions may be adduced as predisposing or concurrent causes of thermic fever. Whatever impairs the animal vigor has this effect. Fatigue, as already noticed, is a potent factor, in man a drinking habit; in all animals a long persistence of the heat during the night as well as the day; impure air in badly ventilated buildings; and mechanical restriction on the freedom of breathing. In military barracks with the daily temperature at 118° F. and the night temperature 105, the mortality became extreme, and in close city car stables the proportion of sun-strokes is enhanced. In all such cases, the air becomes necessarily more and more impure continually. The atmosphere has the same heat as the animal body, so that no upward current from the latter can be established, to create a diffusion. The carbon dioxide and other emanations from the lungs, the exhalations from the skin, dung and urine, accumulate in the air immediately surrounding the animal and respiration becomes increasingly imperfect and difficult. This condition is further aggravated by the accumulation of the animal heat in the body. The blood circulating in the skin can no longer be cooled, to return with refrigerating effect on the interior of the body, the cooling that would come from the evaporation of sweat is obviated by the suppression of that secretion, as well as by the saturation of the zone of air immediately surrounding the body, and thus the tendency is to a steady increase of the body temperature until the limit of viability has been passed.