380 RESPIRATORY METABOLISM 



coma phijormh, and Euglena gracilis. By treating G. piriformis and 

 Polytoma uvella with sodium hydrosulphite and pyridine, he obtained 

 the bands of pyridine-hemochromogen. The observations on Glaucojna 

 are especially interesting because respiration is KCN and CO insensitive, 

 and the explanation of the KCN and CO experiments therefore needs 

 further clarification. Perhaps these organisms contain both cytochrome 

 and a KCN insensitive system (e.g., yellow pigment) which may func- 

 tion interchangeably. This would explain their adaptability to both aerobic 

 and anaerobic conditions, the presence of cytochrome and KCN and CO 

 insensitivity, and perhaps also the somewhat oscillatory character of 

 Colpidium and Glaucoma respiration in the presence of KCN (Pitts, 

 1932; M. Lwoff, 1934). This, of course, is pure speculation. However, 

 the possibility of any discrepancies in the supposed parallelism between 

 CN, CO, and HNo insensitivity and the absence of cytochrome should 

 warrant an intensive investigation. Reidmuller (1936) was unable by 

 spectroscopic methods to find either cytochrome or hemochromogen in 

 Trichomonas foetus, and this result should be expected because of the 

 CO-insensitivity of Trichomonas respiration. 



3. EXPERIMENTS WHICH CONCERN OTHER SYSTEMS OF HYDROGEN AC- 

 CEPTORS 



If we assume that the Warburg-Keilin system is not present in the 

 ciliates, then we must seek another respiratory mechanism. Is this to be 

 found in the action of glutathione? According to M. Lwoff (1934), the 

 effect of arsenious acid on respiration offers a tool for detecting the action 

 of glutathione because it is not supposed to affect the Warburg-Keilin 

 respiratory system and because it does combine with -SH groups, thereby 

 inhibiting the normal functioning of glutathione. In Glaucoma pirifortnis 

 M. Lwoff found that M/1,900 arsenious acid (neutralized sodium ar- 

 senite) inhibited 75-80 percent of the respiration and that M/1,150 

 inhibited 90 percent. The organisms moved slowly in M/400 to M/2,000 

 and remained alive more than thirteen days in M/6,000, but did not 

 multiply. The inhibition of respiration was entirely reversible (recovery 

 in 1 1/2-2 hours from M/2,000). Monoiodoacetic acid, at least in some 

 cases, is supposed to be similar in its action to arsenious acid, that is, it 

 combines with -SH. (In other cases its action may be different, e.g., in 

 the prevention of lactic-acid production from glycogen in muscle extracts 



