Determination of Specific Gravity of Intact Animals by Helium Displacement; Comparison with Water Displacement.

Abstract

Knowledge of the empirical constants relating specific gravity to body fat and body water should permit these quantities to be detd. with moderate precision. A known vol. of He is introduced into a closed chamber of exactly known capacity containing an animal, and the resulting He concn. in the chamber (approx. 20%) is measured by the thermal conductivity method after equilibration with the air in the chamber and that in the animal''s lungs. Then, vol. of He added =vol. of final concn. of added He animal, and specific gravity =wt. of animal. In 10 cats, the vol. of animal avg. difference in specific gravity obtained by the He dilution method and by the method of underwater weighing of the lung-free carcass was 0.013.