Respiration and Metabolism 225 



The mensuration and interpretation of respiratory gas exchange dates back 

 to the signiHcant efforts of Lavoisier, whose work seems to have inspired the 

 notable group to follow, including Seguin, Liebig, Pettenkofer, Voit, and 

 Rubner. Further comparative physiological investigations were stimulated by 

 the careful determinations of oxygen consumption by Regnault and Reiset 

 during the middle of the past century. Today the literature on respiratory 

 measurement— and the field has moved largely into the determination of cell 

 and tissue respiratory mechanisms— is replete with the works of Warburg, 

 Fenn, Linderstrom-Lang, Needham, and others who have designed and 

 developed various types of apparatus to attack significant respiration problems 

 (Fig. 44). 



Determinations of gas exchange and oxygen consumption, particularly, have 

 been made on a great variety of organisms, but owing to the vicissitudes of 

 both animals and techniques the results are sometimes difficult of interpreta- 

 tion. The difference between "standard" and "basal" metabolism,-'^ the 

 variations in oxygen consumption due to size and activity, with the attendant 

 difficulty in attaining "normal" conditions,^^-^ the apparent shift in anaerobic- 

 aerobic respiratory mechanisms induced by experimental procedures-"^'— these 

 and • iher difficulties make the task of presenting representative oxygen con- 

 sumption values a precarious one. Nevertheless some limited data are tabu- 

 lated, which bear on currently significant aspects of comparative physiology. 

 Other extensive surveys of oxygen consumption may be found in the reviews 

 in Tabulae Biologicae by Loewy-''^ and Krebs-*^**- both of whom consider at 

 length tissue as well as organism metabolism— and particularly in the tables 

 in Heilbrunn's Outline of General Physiology. ^^* 



The method of expression of the oxygen consumed presents a problem in 

 itself. A general convention and one that has been followed here is to present 

 the data as cc. oxygen consumed per gm. wet weight of tissue per hour. Such 

 a figure is of considerable comparative value, easily computed from current 

 gasometric data, and readily converted into standard metabolism units. Oxygen 

 consumption may be expressed in terms of grams rather than cubic centi- 

 meters, or as dry (Q02 values) rather than as wet weight of tissue. For some 

 organisms it is convenient to use, in lieu of weight of tissue, numbers of 

 individuals, as the oxygen consumption of Protozoa may be expressed as cc./ 

 million/hr.^^'' ^""^ and of sperm as "Zoo" values— cu. mm. /lO^ sperm/hr.^^ 

 The recent application of the Cartesian diver principle to the determination of 

 live weight of Amoeba has introduced another standard— the O2 consumed 

 (in microliters) per gamma of "reduced weight" per hour, where reduced 

 weight corresponds to the weight of the live object minus the weight of the 

 water displaced. ^^' 



Oxygen Consumption in Relation to Size. Small organisms have higher 

 rates of oxygen consumption than larger organisms when determined both for 

 animals within a given species and for those of closely related phylogenetic 

 groups. Since the days of the early metabolism studies on man, fat people 

 have been recognized as having lower oxygen uptake per unit weight than 

 lean individuals. This has been attributed to the "amount of active proto- 

 plasmic tissue" as the basis for oxygen consumption.-'^ Recent studies of the 

 metabolism of some of the smallest mammals, including shrews weighing 

 3 to 4 grams, give additional evidence for the general rule relating gas exchange 



