361 



corrections which he did make were largely responsible for the superi- 

 ority of his work over that of many others. 



Evidences of a constant total in metabolism. The usual index of the 

 rate of growth and metabolism is the amount of carbon dioxide pro- 

 duced. In the case of insects, the amount produced during definite stages 

 in the life history is probably a constant for an insect of a given weight 

 and species. This has been demonstrated for the pupal stage of the meal 

 worm (Krogh '14). Although the amount given off is a constant total, 

 the rate, however, is not the same throughout the pupal life. It is fairly 

 high at the beginning of the pupal period, falls for the middle pupal 

 period, and rises to a very high rate toward its end. It is obvious, then, 

 that the amount of carbon dioxide given off for a given period is not 

 an index of the amount of progress toward comp'etion of the pupal 

 period unless the amount of progress is ascertained by some other 

 method. It is, therefore, necessary to use units based upon the total 

 amount given off during the time necessary for the completion of the 

 stage. The constant holds good under various tempera' ures. In the case 

 of the meal worm pupa, one degree centigrade within the medial range 

 for one day corresponds to 10/1015 of the total carbon dioxide, or 581. a 

 cc. (At one temperature above the medial range the "degree-day" pro- 

 duced less than this amount.) There is then an actual basis in the meta- 

 bolism of growth and activity for the temperature-velocity units. 



Further evidence as to a basis in activity is found in a recalculation 

 of Crozier's work on the rates at which a centipede crawls at diiTerent 

 temperatures, as shown in Fig. 2, which has already been discussed in 

 PART TWO (pp. 334-337). The form of the curve is the same as 

 that for rate of development. 



The constants for different organisms and for different stages of 

 the same organism are different. Though a given velocity value, i.e., a 

 given number of developmental units per hour, may be shifted a little way 

 up or down the temperature scale in different cases, the effect of one 

 degree remains of the same quantitative value for all organisms within 

 the medial temperatures of each. The constants vary according to the 

 amount of work to be done. 



Evidence from the standpoint of basal metabolism is found in the 

 fact brought out by Krogh ('14b) that the standard metabolism in rela- 

 tion to temperature is the same per imit of weight ( respiratory exchange 

 basis) for a dog as for a fish. The curve for the meal-worm pupa was 

 of the same type and the readings of the same order of magnitude; the 

 only difference was that the entire curve was shifted up the temperature 

 scale.* In this comparison of animals from such radically different groups, 



* The readings were taken when the CO^ output was at a minimum and when 

 respiratory movements and heart beat were also probably at a minimum. This 

 value is more nearly true basal metabolism than the other values. It must be 

 borne in mind that the standard metabolism curve is based upon comparison of 

 metabolism at different temperatures while the pupae were at a particular stage, 

 and that the curves for total growth and development under different temperatures 

 do not agree with the standard metabolism curve at all. 



