174 BIOLOGY OR THE PROTOZOA 



tion, excretion, irritability and reproduction. In Metazoa these are 

 performed by specialized cells, grouped into tissues, organs and 

 organ systems, the complexity varying with the specialization of 

 the organism. In Protozoa they are all performed by the single 

 cell and all are more or less dependent on the activities of the diverse 

 substances and structures which compose it. All work together 

 in a harmonious cycle of matter and energy. 



A. Respiration.— The scientific beginnings of the modern mech- 

 anistic conception of vital activities is traced to Lavoisier and his 

 comparison of animal heat with physical heat due to combustion 

 through oxidation. The utilization of chemical energy, or energy 

 of combination liberated by oxidation, is possibly the keynote to 

 the multiple vital harmonies of animal life (see Yerworn, 1907). 

 Oxygen necessary for such physiological combustion is obtained by 

 all protozoa without the aid of specialized respiratory organs. It 

 is readily absorbed through permeable membranes from the sur- 

 rounding water, or obtained by reduction from oxygen-holding 

 substances, as in anaerobic forms. In one way or another it is 

 ever present to initiate the round of vital functions. 



Oxygen may be taken into the cell directly from the surrounding 

 medium as in the aerobic forms, or it may be obtained by breaking 

 down Oxygen-holding substances, in protoplasm, so-called reducing 

 processes of all types but especially of anaerobic forms. Through 

 the use of chemical indicators the degree of oxidizing power of a 

 cell, including both direct oxidation and reduction, may be deter- 

 mined and is expressed by the symbol rH in values from one to 

 forty. This factor, known as the "oxidation-reduction potential," 

 varies from time to time and is used in much the same way as the 

 expression pH, indicating the hydrogen-ion concentration from 

 intense acidity (pll 1 or 2) to strong alkalinity (pll 10). It is « 

 highly probable that a definite rH is as important for cell activity 

 as a definite pH, and that this oxidation-reduction potential is 

 maintained by the 11 SI I compounds (cystine, cysteine and gluta- 

 thione) of the protoplasm (Krogh, 1916; Hopkins, 1921; Meverhof, 

 1924). 



The intake of oxygen and the voiding of ( !0 2 constitute the essen- 

 tial needs of the cell in respiration. The relationship between the 

 oxygen taken in by an organism and the C0 2 produced by its 

 metabolic activities is indicated by the expression R. Q. (respiration 

 quotient). Daniel, 1931, found that the R. Q. of Balantidium coli 

 under aerobic (sic) conditions is 0.84, which is very nearly the same 

 as the usual R. Q. for man (0.85). For Amoeba proteus and Bleph- 

 arisma undulans Emerson (1929) found the R. Q. to be "about 

 unity." 



To a certain extent the oxygen intake and ( X) 2 output are measur- 

 able, but always with a large experimental error. Kalmus (1927), 



