Definition: two forms. =Heat exhaustion.= Causes: prolonged heat, and moisture, overexertion. Impaired vaso-motor centre. Failing heart. Carbon dioxide poisoning. Symptoms: weak, fluttering pulse, perspiration, muscles flaccid, prostration, no hyperthermia. Treatment: stimulant, digitalis, digitalin, subcutem, nitro-glycerine, warm baths. =Thermic fever.= Hyperthermia excessive. Causes: insolation, prolonged heat and impure air, furnace heat, moist and dry heat, electric tension, overwork, muscular exhaustion, coagulation of myosin, constant heat on one part (head), excess of carbon dioxide, stiffening of bodies when killed in hot weather, debility, weakness, fatigue, chest constriction, tight girths or collars, short bearing reins, plethora, obesity, open cars and yards, fever, privation of water, heavy fleece. Lesions: right heart and systemic veins full, blood black fluid or diffluent, left ventricle empty, congested meninges, effusions in or on brain, or hæmorrhages. Symptoms: =horse=: dull, stupid, stubs toes, sways quarters, droops head, hangs on bit, props on feet, breathes rapidly, pants, stertor, dilated nostrils, gasping, fixed eyes, dilated pupils, tumultuous heartbeats, gorged veins, epistaxis, perspiration, convulsions: =ox=: parallel symptoms: =sheep=: open mouth, stertor, fixed eyes, pupils dilated, panting, swaying, fall, convulsions: =dog=: dull, prostrate, pants, congested veins and mucosæ, weakness, spasms, syncope, speedy rigor mortis. Overheating. Diagnosis: early excessive hyperthermia, venous congestion, shallow panting breathing, violent heart action, loss of sensory and motor functions, convulsions. Prevention: avoid violent, prolonged heat, and exertion, especially in case of fat animals or those new to hot climate, keep emunctories acting, shade head, water on head and to drink, protect fat cattle, shear sheep, water. Treatment: shade and laxatives; if severe, cold water from hose, ice bags to poll, rub legs, acetanilid subcutem, stimulant enemata, later mineral tonics, iron or zinc. _Definition._ A morbid condition produced by the exposure to extreme heat, and marked by profound disorder of the _vaso-motor_ and _heat_ centres. The single term of _sun-stroke_ or _heat-stroke_ has been replaced by two,—=heat exhaustion= and =sun-stroke=, indicating two distinct conditions, brought about by exposure to heat and manifested by different states of the body and distinctive symptoms. Heat Exhaustion.