TRANSACTIONS OF THE SECTIONS. 87 
Experiments on Carbonic Acid thrown. off from the Lungs. By Mr. 
M’GREGOR. 
These experiments, performed by the author while resident in the 
Royal Infirmary of Glasgow, were instituted with a view to ascertain 
whether the quantity of carbonic acid thrown off from the lungs differed 
in health and disease. The mean per cent. in health he found to be 3°5 
per cent., a quantity which very nearly corresponds with that assigned by 
Dr. Thomson of Glasgow, and Dr. Apjohn of Dublin ; that found by the 
former being 3°72 as a mean ultimate result, while that of the latter 
was 3°6. In the eruptive stages of small-pox, measles and scarlet fever, 
the amount of carbonic acid evolved from the lungs was considerably 
increased, in the former to from 6 to 8 per cent., and in the two latter 
to from 4 to 5 per cent. During the aggress and climax of these dis- 
eases, the per centage of carbonic acid showed the above increase, 
while in proportion as convalescence established itself, and the skin 
re-assumed its normal appearance, the per centage of carbonic acid 
gradually diminished. Ten cases of each of the above specified diseases 
were so examined. In chronic skin-disease an augmentation was also 
observed, and in one case of ichthyosis the mean per centage amounted 
to 7°2 per cent. The scaliness.in that case was universal, and ulti- 
mately proved fatal. In diabetes mellitus, a disease in which the ali- 
ment is converted into sugar, and eliminated in the form of urea and 
sugar, no normal aberration could be detected; the carbon in that case 
tae eliminated in the form of sugar and urea. 
Description of a New Instrument for Measuring the Refractive Power 
of Minute Bodies. By ALEXANDER Bryson, of Edinburgh. 
While engaged in a series of experiments on the polarising proper- 
ties of minute crystals, I found that when the microscope was focused 
to the second surface of a plate of glass, on which some minute ery- 
stals of Greenockite were placed, the addition of a thin film of Canada 
balsam spread on the slip of glass, prevented entirely the appearance 
of the Greenockite, until the body of the microscope was raised two 
hundredths of an inch above its former position. 
This property of bodies, with parallel planes, affords a means of ascer- 
taining the approximate refractive power of minute bodies. On this prin- 
ciple Mr. Bryson has constructed an extremely simple microscope. On 
its stage is placed a piece of crown-glass, the refractive power of which 
has been ascertained, having a few fine lines drawn upon its surface with 
a diamond point. If a piece of topaz of ;4,th of an inch in thickness 
is now placed above the lines, it will be found necessary to raise the 
body of the microscope ‘045 of an inch higher than it was while view- 
ing the lines before they can be observed after the interposition of the 
topaz. This difference of focal length then becomes an index to the 
difference of refractive power between the glass plate and the crystal 
of topaz. All that we require is to procure the means of ascertaining 
