318 RESPIRATION 



must be injurious if long-continued or often repeated. This power of adapta- 

 tion is well illustrated by an experiment of Claude Bernard. If a sparrow 

 is placed under a bell-glass of such size that it will live for three hours, be 

 taken out at the end of the second hour (when it could have survived another 

 hour), and a fresh healthy sparrow introduced, the latter will die at once. 



It must be evident that provision for a constant and plentiful supply of 

 fresh air, and the removal of that which is vitiated, are of greater importance 

 than the actual cubic space per person of occupants. Not less than 2,000 

 cubic feet per individual should be allowed in sleeping apartments (bar- 

 racks, hospitals, etc.), and with this allowance the air can be maintained at 

 the proper standard of purity only by such a system of ventilation as pro- 

 vides for the supply of 1,500 to 2,000 cubic feet of fresh air per person per 

 hour. 



Efects of Breathing Gases Other than the Atmosphere. Asphyxiation is 

 produced by the direct poisonous action of such gases as carbon monoxide, 

 which is contained to a considerable amount in common coal gas. The 

 fatal effects often produced by this gas (as accidents from burning charcoal 

 stoves in small, close rooms) are due to its entering into combinations with 

 the hemoglobin of the blood corpuscles and thus preventing the formation 

 of oxyhemoglobin because of the more stable carbon- monoxide hemoglobin. 

 The partial pressure of oxygen in the atmosphere may be considerably in- 

 creased without much effect in displacing the carbon monoxide, hence this 

 is rapidly fatal when breathed. Hydrogen may take the place of nitrogen 

 with no marked ill effect, if the oxygen is in the usual proportions. Sul- 

 phureted hydrogen destroys the hemoglobin of blood and thus produces oxygen 

 starvation. Nitrous oxide acts directly on the nervous system as a narcotic, 

 and may also form a compound with hemoglobin. Certain gases, such as 

 carbon dioxide in more than a certain proportion, sulphurous acid gases, am- 

 monia, and chlorine, produce spasmodic closure of the glottis and prevent 

 respiration. 



Alteration in the Atmospheric Pressure. Lower barometric pres- 

 sures than the normal occur in high altitudes, for example in mountain 

 climbing or in aerial navigation. The susceptibility to decrease in baro- 

 metric pressure varies in different individuals. At an altitude of about 

 10,000 feet many persons begin to experience mountain sickness, though 

 most individuals are not so affected until they ascend to 15,000 feet or 

 more. The symptoms that develop are nausea, dizziness, palpitation of 

 the heart, headache, and muscular weakness. The oxygen partial pres- 

 sure of the atmosphere is reduced to half at about 15,000 feet elevation. 

 At this pressure the body begins to show some stress from inability to 

 get an adequate quantity of oxygen. The tension of the oxygen in the 

 alveolar air is not great enough, see figure 238 showing the relation of the 

 partial pressure of oxygen and the percentage of hemoglobin saturation, 



