406 HEAT-STROKE AND HEAT-EXHAUSTION [VOL. \i Time factor in tion Suitable subject Jvf tion the most refractory of the subjects chosen, fourteen days. This policy is found satisfactory for manual workers, whose active time is divided into shifts, s.vho do not reqaire much technical skill, and who live (out of working hours* and sleep in an equable climate. The medical officers of the WItwarersrand Gold Mines found (Cluver) that fewer casualties from heat occurred among men born and bied in hot climates than among men brought cp in more temperate countries. Wakefield and Hal: < 1 927, a) from their analysis of heat effects among stokers in the American Na\ y. and Mills and Ogle from experiments on animals and an anal} sis of heat effects occurring in the United States of America, also concluded that men brought up in hot environments suffered fewer serious ill effects than men brought up in temperate zones. The ^ell knoiMi resistance of natives of India, tropical Africa, Arabia, and o:her hor climates to hot environments, a resistance usual!\ onl> broken do\\n by malaria or typhoid (Willcox, 1920, a), is an example of perfect acclimatization. The degree of acclimatiza- tion necessary for a worker in the 'brown tropics' (maximum shade temperature about 120' F., dry-bulb, and 72" K, wet-bulb), who not onh works but eats, sleeps, rests, and recreates in his hot environment for months on end, is built up only slowly over a period of months (Marsh. 1935; and depends on many factors in addition to habita- tion to extreme heat. Such acclimatization is near the human limit, and neglect of the process or attempts to hasten it unduly will end in disaster {Marsh, 1935). The induced state Is akin to the condition of an athlete in training. It is well known that bodily fitness for a feat of speed, skill, or endurance can only be acquired very slowly, and pro- ficiency and fitness are easily lost at any stage in the process of prepara- tion if the subject is the \ictim of intercurrent disease, or if he disobeys any of the strict regulations laid down for those in training. Moreover, no athlete will benefit by the most strict training if his mind is not attuned to the process. These considerations apply with almost equal force to the subject for acclimatization, who should be a young adult, free from organic disease or inherited defects, Imbued with correct notions of personal hygiene, and desirous, by reason of some power- ful motive, of undergoing the trials, discomfort, and self-discipline associated with the preparative and fully developed stages of acclima- tization; for this, in its most complete form, is required of any person who undertakes heavy muscular work in extremely hot climatic conditions. To enable the worker to exploit his trained state to the utmost, he must not only be protected from intercurrent disease but have a proper allowance of rest and sleep in moderately cool sur- roundings, sufficient recreation, and a properly adjusted diet contain- ing ample salt, ample supplies of all vitamins, and ample cold pure drinking-water; and he must wear loose airy clothing of thin material, preferably uhite in colour (Gibbs; G. C. Simpson), light, shady, ventilated, and well insulated (aluminium foil, Casteilani and Scotti) head-gear and, out of doors, tinted glasses to neutralize the glare.