108 HARRIET L. ROBBiNS AND C. M. CHILD. 



and region of body these changes in susceptibility are of special 

 interest in connection with the question of the relation between 

 susceptibility and metabolism. If changes in the rate of funda- 

 mental metabolism or of certain fundamental reactions are found 

 to parallel these changes in susceptibility, it is evident that the 

 susceptibility method, when properly used, is a rather delicate 

 indicator of at least certain aspects of metabolic condition. 



In the earlier experiments of Child, as well as in the preliminary 

 work of Robbins, it was found that the changes and differences 

 in CO 2 production following section appeared more clearly in 

 animals which had been starved for a few days before experiment, 

 than in those which had been more recently fed, although in the 

 former the total CO 2 production and oxygen consumption are less 

 than in the latter (Child, 'iqa, Hyman, 'IQ&). It has been pointed 

 out elsewhere (Child, '196, 'igc and various earlier papers), that 

 the susceptibility method as used in these experiments gives in- 

 formation primarily concerning conditions in ectoderm and body 

 wall, though with certain precautions it may be used to show 

 differences in condition in the alimentary tract of Planaria and 

 other forms. The susceptibility data, as well as other facts, 

 indicate that the changes following section are at least in large 

 measure confined to ectoderm and body wall, the alimentary 

 tract not being affected to any great degree. The CC>2 production 

 of the alimentary tract in fed animals constitutes, however, a 

 large proportion of the total CO 2 production, moreover, the 

 volume of the alimentary tract as compared with that of other 

 organs is greater and a larger amount of food and reserves is 

 usually present in regions near the mouth than in regions near 

 the head, therefore it is desirable to decrease this alimentary CO 2 

 production as far as possible, in order that changes in other parts 

 of the body may appear more clearly. It has been shown 

 (Child, 'iga, Hyman, '196) that a rapid decrease in both COa 

 production and oxygen consumption occurs in Planaria doroto- 

 cephala during the first few days of starvation and that an in- 

 crease in both follows so rapidly after even a single feeding that it 

 cannot be due to oxidation of the food following assimilation, 

 but must be due to stimulation of the alimentary tract by the 

 food. Allen ('19) has recently recorded the occurrence of similar 



