PHYSIOLOGICAL BASIS OF PATTERN 47 



the reverse condition. Unless we can eliminate one 

 or the other of these gradients the oxygen consumption 

 and CO 2 production of such pieces is not likely to 

 give us any very definite information as regards either 

 gradient. In this case, however, we can bring the 

 alimentary tract into a more or less quiescent condition 

 by starvation and then we find that a gradient in oxygen 

 consumption and CO 2 production does exist in the body 

 wall, the high end being at the head with a second rise 

 in the region of the posterior zooid. The data along 

 this line are as yet mostly unpublished, but one paper 

 on CO 2 production in Planaria has already appeared 

 (Robbins and Child, 1920) and work on oxygen con- 

 sumption has been done by Dr. Hyman with similar 

 results. But the relative amount of alimentary tract 

 tissue in pieces of a given weight taken near the head is 

 less than in pieces taken near the mouth, so that even 

 in animals which have been starved for some time the 

 difference in total oxygen consumption or total CO 2 

 production of pieces from different regions is not strictly 

 comparable with the regional differences in suscepti- 

 bility of the body wall. Where it has been possible 

 thus far to use these methods we have found that the 

 axial gradients demonstrated by other methods are also 

 gradients in oxygen consumption and CO 2 production. 



EVIDENCE FOR THE EXISTENCE OF PHYSIOLOGICAL 

 GRADIENTS IN VARIOUS ORGANS 



By one method or another or by several different 

 methods the existence of physiological gradients in 

 various axiate organs or parts of many organisms has 

 been demonstrated, e.g., in various reproductive axes 



