No. 4.] CATTLE COMMISSIONERS. 495 



and washing are not the only methods that should be 

 adopted. 



When a ray of light penetrates a dark room, innumerable 

 particles of dust may be seen floating in the air ; these par- 

 ticles of so-called dust are organic matters given off by the 

 occupants of the barn, as well as fungi, bacteria and particles 

 of hay, grasses, etc., which make good carriers for the 

 various forms of bacteria ; and it is this dust that is so 

 dangerous as a source of infection in tuberculosis. 



This can be better realized, perhaps, when it is pointed 

 out that the manure is, and must be considered, one of the 

 dangerous factors by which the disease is spread in the 

 stables : it very frequently contains the tubercle bacilli, and 

 when it dries it becomes pulverized and powdery, and along 

 with the discharges from the nose it mixes with the dust and 

 chafi*, and when stirred up it is carried in the air and is 

 breathed by the cattle, which are frequently kept tied in the 

 barn all winter long without any form of exercise. Under 

 such circumstances the circulation naturally becomes slug- 

 gish, less oxygen is required by the body, the breathing 

 becomes shallow and the lungs are not expanded ; and when 

 any extra strain is put upon them they are unable to do their 

 work, and we have rupture and permanent dilation of the air 

 cells, along with weak lungs and a predisposition to pul- 

 monary disease. In other words, we have just the condition 

 most suited to the development of tuberculosis, and at the 

 same time the animal is breathing an atmosphere impregnated 

 with infectious material. 



Bearing this in mind, then, one can readily see how im- 

 portant it is to thoroughly ventilate the barns. When the 

 hot, foul, infected air is continually being diluted by fresh 

 outside air, of course the continual dilution lessens the 

 proportional amount of infectious material in the air, and 

 therefore lessens the danger from its inhalation ; and not 

 only is there less danger from infection, but the health of 

 the animals is better. When only a small quantity of Cog 

 is contained in the air, the Cog in the lungs is very readily 

 difi'used through the atmosphere ; but when that atmosphere 

 has become impure, when it contains a large quantity of Co., 

 with organic impurities, then the C02 in the lungs is not so 



