378 RESPIRATORY METABOLISM 



at a concentration of M/lOO KCN. Von Fenyvessy and Reiner (1928), 

 however, reported no effect with 0.1 percent KCN (M/65) on either 

 oxygen consumption or acid production of Trypanosoma equiperdum in 

 glucose-bicarbonate-Ringer solution. 



These results demonstrate that the respiratory mechanisms of various 

 Protozoa are probably not the same. The respiratory mechanisms of some 

 Protozoa seem to resemble those of Chlorella and Sarcina, while those 

 of other species resemble the mechanisms of yeast and mammalian and 

 other tissues. This question is one which should be studied carefully 

 in a wide variety of organisms, and with a wide concentration range 

 of cyanide solutions. The taxonomic position of the Protozoa should 

 make such an investigation doubly interesting. It would also be of 

 interest to know if the cyanide insensitivity of Paramecium is still main- 

 tained in the presence of glucose and other substances, or if an apparent 

 change in the respiratory mechanism is brought about by the presence 

 of glucose. Emerson (1929) found that the respiration of Chlorella was 

 cyanide sensitive only in the presence of glucose; Gerard (1931) found 

 that glucose had no effect on the cyanide sensitivity of Sarcina, but 

 M. Lwoff (1934) found that the respiration of Glaucoma was accelerated 

 by HCN when glucose was absent. These divergent results should have 

 a final explanation in terms of the respiratory or other metabolic mecha- 

 nisms involved. 



An alternative theory to the supposed coexistence of cyanide sensitive 

 and insensitive fractions in the normal cell is that all normal respiration 

 is CN sensitive, and that in the presence of CN an entirely new 

 respiratory mechanism is called into existence. This interpretation would 

 indicate that among many bacteria, algae, and ciliates (but not among 

 certain flagellates) there is a greater adaptability of the respiratory 

 mechanism than among the more specialized cells of the Metazoa. Such 

 generalizations are probably premature, but it does seem possible that 

 aerobic protozoa which can live anaerobically for considerable periods 

 of time might have a dual respiratory mechanism. 



It has been demonstrated for several biological materials that respira- 

 tion sensitive to cyanide is also sensitive to CO (because of CO-inhibi- 

 tion of cytochrome oxidase), and that respiration insensitive to cyanide 

 is not depressed and may even be stimulated by CO (literature cited 

 by Bodine and Boell, 1934). A. Lwoff (1933) showed that the KCN 



