RESPIRATION. THE GASEOUS INTERCHANGES 427 



be safe in assuming the point of onset of marked respiratory dis- 

 tress as indicating the passage of the laboring muscles beyond the 

 limit at which their immediate need for oxygen can be fully sup- 

 plied. 



Coal Gas Poisoning. In the paragraph on asphyxia (Chap. 

 XXIII) the possibility of suffocation by carbon monoxid was 

 mentioned. This substance, which is an important constituent of 

 illuminating gas, has a greater affinity for hemoglobin than has 

 oxygen, and forms with it a more stable compound, carbon monoxid 

 hemoglobin. The result of breathing illuminating gas is, then, the 

 conversion of hemoglobin of the blood into carbon monoxid hemo- 

 globin, and the consequent abolishment of the oxygen-carrying 

 function of the red corpuscles. If the breathing of carbon monoxid 

 has gone on long enough for practically all the hemoglobin of the 

 blood to be combined with it, death from lack of oxygen is inevit- 

 able unless by the prompt performance of blood transfusion a 

 fresh supply of properly functioning red corpuscles be introduced 

 into the circulation. Exposure to the gas for a shorter time, not 

 enough to prove fatal, but to the point of unconsciousness, is often 

 followed by a long period, weeks or months, of serious functional 

 impairment of the tissues of the Body, due to the injury suffered 

 by them during the period of oxygen deficiency. 



