APPENDIXES 



731 



makes the remarkable statement that the ratio of oxygen consumption in different 

 pieces "was just about the same as the relative amount of movement of these parts 

 during the course of the measurements." In a determination on anterior and posterior 

 halves of Thysanozoon the pieces remained 48 hours in the respiratory chamber before 

 determinations and had apparently come to rest, but "some movement invariably 

 took place at long intervals." In this case the oxygen consumption of the posterior 

 half was 26 per cent less than that of the anterior half. The question whether some 

 movement at long intervals is sufficient to account for so great a difference is not con- 

 sidered. In view of the obvious lack of the precautions necessary in determinations of 

 this sort, Shearer's data cannot be regarded as having any significance whatever, and 

 certainly not as valid evidence against the highly consistent data which have been 

 obtained in repeated experiments performed with proper care. 



The method of comparative estimation of CO2 production used with planarians 

 and with Corymorpha has been criticized by Parker (1929) and by Needham (1931, 

 p. 586) on the ground that precautions were not taken "to ensure that the acidity 

 measured was due to carbon dioxide and not to other acids." Whether other nongase- 

 ous or nonvolatile acids or acid-producing substances than CO2 are produced is 

 easily determined by bubbling air through the indicator solution or by allowing it to 

 stand exposed to air in a thin layer after change in color by, and removal of, animals 

 or pieces. In one of the earlier papers concerned with this method attention was called 

 to this point, and it was stated that with this procedure the color does return (Child, 

 igigb). It was not considered necessary to repeat this statement in later papers; but 

 the test was consistently made, and consequently the criticisms are not justified. 

 With this method the material is undisturbed during the respiratory period, but the 

 method used by Parker involves continuous movement of the apparatus, and a small 

 amount of water is desirable. With sluggish forms like Stylochus (Watanabe and Child, 

 1933) consistent results can be obtained. Parker says, regarding the planarian pieces 

 used in his experiments: "Ordinarily they remained quietly in the bottom of the 

 scoop," and, as regards Nereis pieces, that they "remained in relative quiescence." 

 Here, as in the respirometer methods, the question of the efifect of motor activity on 

 respiration arises. There can be no doubt that with the Winkler method motor activity 

 is less than with the other methods used in work of the kind under consideration; 

 also, the use of a considerable number of pieces eliminates or decreases the elTect of 

 individual differences. At best, however, respiratory determinations on pieces from 

 different body-levels of adult animals constitute only contributory evidence on the 

 gradient problem, but their close agreement with other lines of evidence increases 

 their value. 



For further critical discussion see Watanabe and Child, 1933. 



