From: The physical examination of the chest in pulmonary consumption and its intercurrent diseases by Somerville Scott Alison. 1861. Page 351.

“This instrument differs from Hutchinson’s in principal, and possesses the advantage of equal accuracy, great portability and comparative cheapness. It consists of two bags, one acting as a reservoir for expired air, and the other as a measure. The air is first expired into the larger back supplied with stopcocks to retain it. The next step is to pass seriatim the air into the measure bag, and to calculate the amount. The second bag can contain from 40 to 50 cubic inches, and it is to be filled from time to time, till the whole amount is measured. This instrument only costs 26s., and Mr. Coxeter I understand, has very recently improved it.”