586 ON INCREASE IN COMPLEXITY [pt. iii 



It is clear that the only methods capable of informing us whether 

 gradients of metabolic rate are involved (cubic millimetres of 

 oxygen used up per gram per hour or cubic millimetres of carbon 

 dioxide given off per gram per hour) are direct estimations of these 

 gases. Yet out of the hundred odd papers which make up the core 

 of the literature on physiological gradients, not more than a dozen 

 at the very outside are concerned with these fundamental measure- 

 ments. In 1915, when Child's first two books were published, the 

 only evidence available was due to Tashiro, who had, at Child's 

 request, examined the behaviour of planarian worms in his micro- 

 respirometer, and had concluded that the pieces from the cephalic 

 end gave off more carbon dioxide relatively than those from the 

 caudal end, though the figures seem never to have been published. 

 In view of the criticisms which Adam; Bayliss; and later Parker 

 brought against Tashiro's apparatus, not much weight can be 

 attached to these results. 



In 1 92 1 Robbins & Child obtained evidence from a study of 

 regeneration in planarian worms that the larger amount of carbon 

 dioxide was produced relatively at the head end, and in the following 

 year Hyman & Galigher reported the same relationship to hold 

 as regards oxygen for the oligochaete worms Lumbriculus inconstans 

 and Nereis virens. Preliminary results on Corymorpha palma, a large 

 tubularian hydroid, were given by Child & Hyman to the American 

 Zoological Society in 1922 and 1923, and published in extenso by 

 Child & Hyman in 1926. Hyman extended this to oxygen uptake 

 of planarians in 1923. Her results were paralleled by figures for 

 carbon dioxide production estimated by a colorimetric method in 

 which the time taken by pieces of the stem to reach a definite acidity 

 was measured. But no precautions were used to ensure that the 

 acidity measured was due to carbon dioxide and not to other acids, 

 for the method did not involve passing a stream of air through the 

 water containing the stem under investigation. The oxygen deter- 

 minations, on the other hand, were all done by the Winkler method, 

 and were never checked by any differential manometer technique. 

 That this is a serious deficiency is evident from the remarks of 

 Shearer, who in a private communication says, "With Haldane's 

 and Barcroft's apparatus I could not get any results which even 

 begin to support Hyman's tables. I think that the Winkler method 

 is useless where a lot of slime is discharged into the water (as is the 



