Respiratory Functions of Body Fhiids 



321 



to make all of the aforementioned tests. Evidence is sufficient, however, to 

 shoH^ that in some lower animals blood pigment functions in O^ transport at 

 all oxygen tensions as in the vertebrates, in some it functions in. transport only 

 at low tensions, in others it may be an oxygen store for use in periods of 

 hypoxia, and in still others it has no function with respect to oxygen supply. 



In Lumbricus, Chironomus, and Tuhifex carbon monoxide poisoning dem- 

 onstrates the transport function of hemoglobin. In monoxide experiments it 

 is important that the maintained combination of the hemoglobin with CO be 



Op IN MM. HG 



Fig. 76. Oxygen dissociation curves of several species of amphibians. 

 From McCutcheon and Hall.'" 



checked spectroscopically, and that the amounts of CO used be small enough 

 that there is no interference with tissue respiration. In the earthworm, oxygen 

 consumption has been measured in three investigations at different oxygen 

 tensions in the presence and absence of carbon monoxide. One study^^^ 

 revealed no effect of CO on respiration. Another''' showed little effect of CO 

 in reducing the respiration down to an Oo tension of about 55 mm. (7.5 per 

 cent O2), but below that value there was some reduction in Oo consumption. 

 In the most careful study,'-'" saturation of the hemoglobin by CO was checked 

 systematically and it was found that the respiration was reduced by CO at high 



