Heat acclimatization by a method utilizing microclimate cooling.

A new approach to heat acclimatization has been shown to be feasible during laboratory experimentation. Wearing microclimate suits containing dry ice as the coolant, three groups of men were subjected to a moderate work rate in three different environments for 4 h/d for 8 d. Physiological responses on a subsequent heat tolerance test indicate that the group subjected to an environment of 32.0 degrees C W. B. and 33.5 degrees C D.B. were fully heat acclimatized. The 33/35 degrees C group were also well-acclimatized but developed dangerously high body temperatures during the first 2 d. Only partial acclimatization was achieved by the 31/33 degrees C group. The reason why the men acquire heat acclimatization while wearing the microclimate suits in a hot environment is probably that microclimate cooling does not prevent body temperature from rising--it only prevents it from rising excessively. It should be remembered that only one-third of the body is cooled while the rest shows the normal sweating response.

Effect of blood vitamin A levels on the dark adaptation of mineworkers.

The average dark adaptation time for newly recruited Black mineworkers is longer than that reported for Whites. While this longer dark adaptation time may result from a number of pathological conditions, its most likely cause is a deficiency of vitamin A in the diet. A study was conducted in which the vitamin A level of the blood and the dark adaptation times were correlated in a group of Black mineworkers upon arrival and again after 4 - 6 months continuous work underground in a gold mine. The study indicated that a very marked decrease occurred in the miners' serum vitamin A level between the time of arrival at the mine and the second examination. This difference was found to be highly significant. This decrease was accompanied by an increase in mean dark adaptation time, which was significant at the 5% level. These observations accord with the findings of a previous study and are indicative of an inadequate dietary intake of vitamin A during the period when the miners were on the mine diet.