SANITARY CONDITIONS OF DAIRY EARMS. 
467 
as fifty or sixty parts of co 2 in 10,000, and, I have no doubt, if 
the percentage was taken during cold weather in winter, when 
the barns are tightly shut up, the air would be very much worse. 
When only a small quantity of co 2 is contained in the air, the 
CO2 in the lungs is readily diffused through the atmosphere ; but 
when that atmosphere has become impure, when it contains a 
large amount of co 2 with organic impurities, then the co 2 in the 
lungs is not so readily diffused through the air ; it has found it 
level and is retained in the system where it lowers the vitality, 
causing the dullness and lethargy experienced by any one after 
sleeping all night in a close room. 
In calculating the amount of impurity in the atmosphere of 
a barn, the co 2 is taken as a standard of impurity, only because 
so far no simple means has been discovered by which the other 
impurities can be determined, so that the amount of co 2 shows 
only relatively the amount of impurity in the air. 
When a ray of light penetrates a dark room, innumerable 
particles are seen floating in the air. These particles of so- 
called dust are organic matters given off by the occupants of the 
barn as well as fungi, bacteria, dried manure and particles of 
hay and grasses. It is this dust that is so dangerous as a source 
of infection in tuberculosis. The manure, as pointed out by 
Billings, contains the bacilli; when dry it becomes pulverized 
and powdery, and, along with the discharges from the nose, it 
mixes with the dust and chaff and the other impurities in the air 
which are breathed by the cattle. Ventilation, which should 
rid the atmosphere in the barn of these impurities, being alto¬ 
gether lacking. 
Drainage, dark and damp cellars under the barns have a 
close relationship to the ventilation and warmth of the barn. 
The wet and filth usually found in a cellar, keep the air of the 
barn damp and chilly; while the decomposing animal and vege¬ 
table matters give off a quantity of co 2 which contribute largely 
to swell the amount already in the barn. 
The cellar is considered by many farmers to be a necessity. 
There the manure is kept; there odd tools and implements are 
