Abstract
Experiments upon normal dogs, kept at rest in hot and cold baths up to the neck, have shown regular changes in total blood solids. Blood solids were determined simply by weighing a sample of 15-16 drops shed freely from the ear vein and drying to constant weight.
Exposure to hot baths for various intervals is illustrated by Table I, to cold baths by Table II.
It will be seen from the tables that normal dogs respond regularly to a moderately high environmental temperature by hemodilution and to a cold environment by hemo-concentration. Roughly, the change usually approximates 2 per cent. of the total blood weight, which means a 10 per cent. change in the fluid content of the blood.
The circulatory factor in regulation against overheating and cooling consists not merely in transferring of blood respectively to or from the body surface but also in actual shifting of water into or out of the blood stream. The response to a hot environment is peripheral vasodilation plus hernodilution; a cold environment evokes vasoconstriction plus hemoconcentration.
To simplify the above presentation the rectal temperature readings have been omitted; these showed in the case of the cold baths and sometimes in the case of the hot, that the bath conditions were too extreme for the animal to withstand in spite of the regulatory responses.
Confirmatory evidence has been accumulated since the above experiments were carried out.
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