The Aborigines of Central Australia live under conditions of high temperature and low humidity during a considerable part of the year. The periods during which they are most likely to suffer from lack of water are those in which from physiological considerations they should need more of it. They must often lose, not only the whole of their heat production by evaporation, but also what they absorb, owing to high external temperatures. They should need more water than persons in temperate, well watered regions, unless they have developed some means of sparing it. They are indeed able under certain conditions to reduce both their voluntary activity and their basal heat production very materially (Wardlaw and Horsley, 1928), but in their natural state it cannot be possible for them to lead a very slothful existence. These two means of sparing heat production are not independent, as several investigators have shown (Benedict and Smith, 1915; Osio de Almeida, 1920; Wishart, 1827). This is very evident in Australian aborigines (Warlaw and Lawrence, 1932).

In the present investigation the measurement of the proportion of the basal heat loss from the body by evaporation has been the principal object. A few measurements have been made under conditions other than basal and over periods up to twenty-four hours.

The Aboriginal Subjects.

• Tribe: With the exception of Nos. 3, 4, and 14, who were full-blood Aranda, the subjects were full-blood Aluritja.
• Age and Sex: Adult males.
• Activity: No regular physical activity was allowed during the period of observation. Up to that time the Aluritja had been living under natural conditions. The Aranda had been employed as stockmen.
• Diet: This consisted of 450gm. flour, 80gm. sugar, and a little tea as rations, supplemented to an unknown extent by rabbits; no hunting was engaged in, nor was any attempt made to collect native vegetable foods.
• Health: With the exception of No. 13 (who showed signs of nephritis) and No. 22 (who showed signs of yaws), the subjects were in normal health and had not recently suffered from any illness.
• Climatic Conditions: These are summarized in Table 1. In brief, the region was hotter, drier, and higher than those in which the previous observations were made. The small difference between the average temperatures at which the basal observations were made in Sydney and Hermannsburg is due to the fact that the Sydney observations were made much later in the morning.

The White Subjects.

The same measurements were made on these as on the aborigines. Their activity and diet in Central Australia were not significantly different from what they were in Sydney.

Physique and State of Nutrition.

The heights and weights of the nude subjects are recorded to 0.5 cm. and 0.2 kg. The weights are also expressed as percentages of the weights for given heights and ages reported by Hunter (1912). The ages had to be assessed. The effect of age on weight is more important in the younger subjects, but it is not likely that the assessed ages were outside of the correct five-year age groups of the tables used.

The sitting heights (knees drawn up) were also recorded to 0.5 cm. and the pelidisi calculated.

Basal Metabolism.

The Haldane-Douglas method was used under conditions similar to those of previous investigations (Wardlaw and others. loc.cit.)

Although the subjects were co-operative, many repetitions were necessary with some before evidence of steadiness was obtained. Even then some R.Q.'s showed evidence of over-breathing. The values must therefore be regarded as maximal. Results differing by more than 5 p.c. from the mean were rejected.

Insensible Perspiration.

For basal measurements the subjects were weighed before and after about 30-minute periods (Benedict and Root. 1926)

The Australian Journal of Experimental Biology and Medical Science. (1934) Vol. XII.