Physiology 453 



should be interpreted cautiously, since extensive variations apparently 

 occur even in single species. For example, oxygen consumption of Para- 

 meciiun caudatum has been recorded as 0.00014 (339), 0.0004 (213) and 

 0.0052 mm-'^/hour/organism (266). In addition to differences attributable 

 to different manometric techniques, the physiological condition of the 

 test organisms may be a significant factor. Starvation significantly reduces 

 oxygen consumption of Paramecium caudatum (339) and Pelomyxa caro- 

 Unensis (526). Likewise, a marked decrease occurs in old cultures of 

 Colpidhnyi colpoda (563), Bodo caudatus (310), Chilomonas paramechim 

 (221), Tetrahymena pyrijormis (9, 431), Trichomonas foetus (484), and 

 Trypanosoma cruzi (33). In T. pyriformis the change occurs after the 

 logarithmic phase of growth (421) and is not correlated with any decrease 

 in cytochrome content (9). Changes in consumption also have been traced 

 during conjugation of Paramecium caudatum (585). 



Environmental conditions also may influence oxygen consumption. For 

 Tetrahymena pyriformis consumption is at a maximum in media at pH 

 5.5 and is distinctly lower on each side of the optimum (170). Increasing 

 temperatures, within physiological limits, stimulate oxygen consumption 

 of ciliates (267, 563) and Strigomonas fasciculata (341). The oxygen con- 

 sumption of Spirostomum ambiguum increases with increasing oxygen 

 concentration of the atmosphere to which cultures are exposed. The maxi- 

 minn, observed with pure oxygen, was about 50 per cent higher than for 

 ciliates exposed to air (532). On the other hand, changes in oxygen 

 tension within fairly wide limits have produced little effect on Para- 

 mecium caudatum (4). 



Respiratory quotients 



The ratio of the carbon dioxide produced to the oxygen consumed 

 — the respiratory quotient (R.Q.) — has interested physiologists as a theo- 

 retical index to the type of material being consumed. The R.Q. for com- 

 plete oxidation of carbohydrate is 1.0 and is about the same for acetate; 

 for butyrate, about 0.8; for fats, approximately 0.7; for proteins, about 0.8 

 (urea as the nitrogenous waste) or about 0.9 (ammonia as the nitrogenous 

 waste). Quotients well above I.O may indicate synthesis and storage of fat 

 produced from carbohydrate. Low values (0.4-0.6) might indicate con- 

 version of protein to carbohydrate, or incomplete oxidation of carbo- 

 hydrate. 



Most of the R.Q. values reported for Protozoa (Table 8. 4) fall within 

 the usual range. This is especially true of Trypanosomidae, some of which 

 have shown a higher R.Q. with glucose than without (415, 531), as would 

 be expected. Unusually low values for several phytoflagellates have been 

 attributed to synthesis of carbohydrates from carbon dioxide (398) and 

 to the conversion of protein into carbohydrate or the incomplete oxida- 

 tion of carbohydrate (247). Varying quotients for a species may reflect 



