RESPIRATION 201 



fluence of excitement or exertion, the breathing becomes more 

 frequent and more profound ; and then the internal respiratory 

 work increases proportionately, and may even be double that 

 of the above estimate. It has been estimated that in drawing 

 a full breath, a man exerts a muscular force equal to raising 

 two hundred pounds placed upon the chest. 



28. Impurities of the Air. The oxygen in the atmosphere 

 is of such prime importance, and its proportion is so nicely 

 adjusted to the wants of man, that any gas or volatile substance 

 which supplants it must be regarded as a hurtful impurity. 

 All gases, however, are not alike injurious. Some, if inhaled, 

 are necessarily fatal ; arsenuretted hydrogen being one of these, 

 a single bubble of which destroyed the life of its discoverer, 

 Gehlen. Others are not directly dangerous, but because they 

 take the place of oxygen, and exclude it from the lungs, they 

 do harm, and become dangerous. To this latter class belongs 

 carbonic acid gas. 



29. Most of the actively poisonous gases have a pungent or 

 offensive odor ; and, as may be inferred, most repugnant odors 

 indicate the presence of substances unfit for respiration. 

 Accordingly, as we cannot see or taste these impurities, the 

 sense of smell is our principal safeguard against them. In this 

 we recognize the forethought which has stationed this sense, 

 like a sentinel, at the proper entrance of the air-passages, to 

 give us warning of approaching harm. Take, as an example, 

 the ordinary illuminating gas of cities, from which so many 

 accidents happen. How many more deaths would it cause if, 

 when a leak occurs, we were not able to discover the escape of 

 the gas by means of its disagreeable odor. (Head Notes 5 and 6.) 



5. Cleanliness the Sum Total of Hygiene. " Disinfectants have 

 the power of destroying the cause, and of arresting the spread of most 

 epidemics and contagious diseases, but cleanliness is the best preventive 

 of disease. Whenever practicable, the abundant use of water is better 

 than disinfection. ' Let no one ever depend upon disinfectants, fumiga- 

 tions, and the like, for purifying the air. The offensive thing, not its 

 smell, must be removed.' " Flore nee Nightingale, Notes on Nursing 

 (in part). 



28. Importance of the oxygen in the atmosphere ? Injurious character of gases ? 



29. Pungency of gases ? The inference ? Our safeguard ? 



