RESPIRATION 



167 



as serious symptoms began to develop after administration of the 

 dose, placed the animals in compressed oxygen. The result was 

 that the serious symptoms disappeared and the animals recovered. 

 If, however, they were removed into ordinary air, they died at 

 once with anoxaemic convulsions. When kept in the oxygen for a 

 sufficient time, however, they completely recovered and could be 

 returned to ordinary air. Oxygen at ordinary atmospheric pres- 

 sure was often sufficient to save the animals. 



Having worked out a method for estimating colorimetrically 

 the proportional extent to which the haemoglobin was altered by 

 the poison, we then found that the dangerous symptoms depended, 

 just as in CO poisoning, on the extent of the alteration. It was 

 thus evident that the cause of death, and of the dangerous symp- 

 toms, was anoxaemia, just as in CO poisoning. We also found that 

 the methaemoglobin and NO haemoglobin soon disappeared, leav- 

 ing the blood quite normal, if death was averted. The methaemo- 



IOO 



70 



^ 



60 



50 



I 



^ 40 

 1 



20 

 10 



Mours offer srr/'ec{t'o/i 



Figure 53. 

 Methaemoglobin due to sodium nitrate. 



globin was simply reduced back again, just as on the addition of 

 a reducing agent to a methaemoglobin solution outside the body. 

 It was also evident that the reduction process was constantly going 

 on and tending to neutralize the poison even while the relatively 

 large amounts of it were still present in the blood. In proportion 



