200 
MEMOIRS OF A VETERINARY SURGEON. 
kind of organic matter is "wholesome or otherwise; it has, 
nevertheless, laid bare numerous facts calculated to stimulate 
future inquiry, and it is more than conjectured that by it we 
may even hope to perceive premonitory causes of disease 
in the atmosphere before they affect the human body. The 
exciting cause itself exists long before it has been able to take 
effect, so that useful precautions may be made in time, and 
an efficient defence prepared. 
The instrument is described as follows by the inventor: 
“The vessel used is simply a bottle with a perforated 
stopper, through which pass two tubes, to one of these a stop¬ 
cock is attached, to the other a clasp or stop-cock. The standard 
size proposed is 100 cubic inches,and to this all the experiments 
have been reduced. The stop-cock is of glass, or hard caout¬ 
chouc, which is still better. When the bottle is to be filled with 
air to be tested, the stopper is removed and the pipe of an 
exhausting pump is inserted, reaching to the bottom of the 
bottle. The pump is made like a cylindrical bellows, of about 
eight inches long when stretched out, and about four inches 
in diameter, and is compressible into the thickness of about 
two inches ; the sides are made of thin mackintosh cloth. By 
the use of the pump the air of the vessel is removed and the 
external air of course enters; a few strokes of the pump are 
sufficient, i.e ., from six to ten. After ten strokes I perceive no 
change, and am inclined to think that it is an unnecessary 
number. The test liquid is poured into a graduated tube, or 
buvette, containing somewhat more than will be required. 
A portion is then poured into the tube which passes through 
the stopper, and the stop-cock is opened to allow it to pass; 
small quantities are used. When it has entered the bottle the 
liquid is made to spread over the sides, and time given it to 
be exposed to the action of the air. It is found that in five 
or six minutes a decided epoch is attained from which to 
date the comparative action. The first few drops that are 
poured in will probably be decolorised at once, a few more 
drops must then be added, if they become decolorised a few 
drops more must be used, and so on until there is a per¬ 
ceptible amount of colour remaining. When this occurs the 
experiment is concluded. The amount of the reagent used 
is then to be read off from the graduated measure, the 
number of grains gives the comparative quantity at once. 
“ If the matter in the air be in a decomposing state the 
colour of the test is rapidly destroyed, but if the matter be 
not in a state of decomposition the action will be much 
slower. 
“The liquid test is an extremely weak solution of the 
