RESPIRATION 217 



indeed, is that either an excess of C0 2 or a deficiency of 

 oxygen is injurious. The former acts as a narcotic 

 poison, but it does not begin to exert its effects until 

 3 per cent, is present, an amount which is never reached 

 even in a very ' stuffy ' room. It is to deficiency of 

 oxygen that the effects of breathing a limited quantity 

 of air and the phenomena of asphyxia are due, but here, 

 again, it is not until the proportion of oxygen is reduced 

 to about 10 per cent, that any bad symptoms manifest 

 themselves. Reviewing the whole subject, even such a 

 careful and experienced worker in this department as 

 Professor Haldane is able to come to no more satisfactory 

 conclusion than that the headache, lassitude, etc., which 

 are experienced in a badly ventilated room are not due 

 either to want of oxygen or to the presence of an excess 

 of C0 2 , but that they are partly the result of heat and 

 moisture, and partly, perhaps, produced reflexly through 

 the olfactory nerves.* 



An interesting point in connection with this subject is 

 that much-breathed air is more injurious to healthy, 

 vigorous animals than to those which are feeble and 

 exhausted. If, for example, a sparrow is confined in a 

 bell jar for a matter of two hours it will still be alive 

 and fairly vigorous. A second sparrow now introduced, 

 however, dies at once. It would thus appear as if an 

 animal can accommodate itself to oxygen starvation, 

 probably by a general lowering of its metabolism, but in 

 part also, perhaps, by an increased power of absorbing 



* Hale White's ' System of Pharmacology.' The proportion of 

 C0 2 in an inhabited room should not exceed 12 parts per 10,000 

 during daylight, and 20 parts per 10,000 when gaslight is used. 



