VENTILATION 111 



student may safely take their statements as correct in a general 

 Avay, but may just as safely doubt the usual explanation. 



Work done at the Minnesota Experiment Station seems to 

 demonstrate quite conclusively that the accepted explanations 

 are incorrect; that any probable increase of CO2 or any prob- 

 able decrease of oxyg-en are not especially important. This 

 work seems to show that the injury comes from entirely dif- 

 ferent factors. 



The :\linnesota Station has had a number of different animals 

 continue apparently in good health when confined for consid- 

 erable periods in very high percentages of COo. In one case a 

 steer made good gains, was bright and active, and showed no 

 important physiological disturbances when long confined in air 

 containing COo, ranging as high as 2.67 per cent, or nearly 90 

 times the average for outside air. 



Experimental work shows that decrease of oxygen does not 

 lessen the amount absorbed by the animal until we reach the 

 very low level of about 13 per cent, 20.97 per cent being taken 

 as a normal. But 13 volumes per cent is much lower than would 

 be found in any stable. 



Excretion of CO, may be checked and difficult respiration 

 occur in case of very great excess of this gas. It has been 

 found by other experimenters that when the air contains from 

 3 to 4 volumes per cent of CO. the excretion of gas might be 

 checked 50 per cent, with no harmful effect detected. The ex- 

 cretion of CO2 is practically independent of percentage of 

 oxygen in the air. One very good authority tells us that tissue 

 metabolism is not disturbed by variation of oxygen above 10.5. 

 Below 10.5 percentage of oxygen there were marked physiologi- 

 cal disturbances; but this is far below any probable stable per- 

 centage. 



There does not appear to be any good reason for doubting 

 the importance of stable ventilation. It is equally plain, how- 

 ever, that the injurious effects of unventilated air in common 

 stables does not come from high COo or low oxygen percentages, 

 and that we must seek the explanation in other directions. 



Accumulation of liarmful germs gives a portion of the ex- 

 planation. Modern research shows that 11i<' physical condition 

 of the air, rather than the chemical composition, is the impor- 

 tant factor. Aside from bacterial content of the air and irri- 

 tating substances, the important thing in ventilation is the con- 



