357 
tfeat no aeriform fluid, but also that no carbonic 
matter is exhaled by the human skin. 
667. Adverse, however, as these experiments seem 
to the opinion that the oxygen gas of the air is af- 
fected by the human skin, yet, in others lately made 
by Dr Charles Mackenzie, and which we had an op- 
portunity of witnessing, carbonic acid was clearly de- 
tected in tiir that had been kept for two hours in 
contact with the skin. Dr Mackenzie confined his 
hand and wrist in a glass vessel which contained 
about 50 cubic inches of atmospheric air. Around 
the mouth of the vessel a piece of oiled silk was fas- 
tened, through which the hand was introduced, and 
the silk cloth was then closely secured round the 
arm above, so as to cut off the communication with 
the external air. In a few minutes the inside of the 
vessel was bedewed with moisture, which, during 
the experiment, accumulated to the quantity of near- 
ly half an ounce. The experiment was conducted 
in a warm room, and was continued for rather .more 
than two hours. In order to examine the air, the 
hand, with the glass vessel still attached to it, was 
plunged under water in a pneumatic trough, and the 
oiled silk being then removed from the arm, the hand 
was withdrawn. A portion of the air was now pass- 
ed from the glass vessel into a small tube filled with 
pure lime-water. It did not affect t}ie lime-water in 
its transmission through it, but a white filmy crust 
formed on those parts of the sides of the tube from 
which the lime-water had been expelled, and in a 
minute or two, white threads of carbonate of lime 
likewise fell down through the mass of fluid. The 
