Differences in Physiological Activity in Brown and White Fat as Revealed by Histochemical Reactions

Abstract

A method of measuring C14 by converting it to CO2 is descr. To make CO2 suitable as counter-filling gas, a second component such as CS2 was added. G-M counter tubes were used with a stabilized high-voltage power supply with an output up to 5,000 V., modified Neher-Pickering preamplifier, scale of 128, Cenco register, and electric timer. CO2 was at any pressure from 10 to 50 cm. Hg. with CS2 vapor to represent 2 cm. pressure within the counter tube. The measured counting rate per unit amt. of active CO2 was found to be a function only of the amt. of activity within the counter tube. If the counting rate was corrected by the ratio of the total volume of the counter to the volume defined by the cylindrical cathode, all counter tubes within the size range used showed . the same response to equal amts. of activity within the counters. The non-linearity correction for these counters amounted to 12% loss at 10,000 C.p.m. and was derived from a curve made by adding increment amts. of active CO2 to a counter tube and plotting counting rate less background against arbitrary units of active CO2 in the counter tube. Measured amts. of inert and active CO2 were mixed. The samples of activity were drawn from a bulb containing radioactive CO2. The sample was distilled into a counter tube and CS2 vapor was added. The counting rate was detd. at 160 V above threshold. Background rate was detd. in the same counter filled with inert CO2. The corrected counting rate was detd. by subtracting background from the observed rate, multiplying this by the ratio of the total volume of the counter to the cathode volume to correct for that fraction which was not within the sensitive volume of the tube, and then correcting this figure for the non-linearity of the counters. With an avg. deviation of 3%, the system allowed the direct comparison of activities of a large range of sample sizes.