52 C. M. CHILD. 



between the different groups of facts is strikingly evident. The 

 degree of morphological and physiological "cephalization" in 

 these infusoria parallels the degree of difference between the 

 rate of metabolism in the apical region and that in other regions. 

 The obvious inference from the facts is that the axial metabolic 

 gradient has some very intimate relation to the morphological 

 and physiological polarity of these organisms. 



The occasional departures from the general rule such as the 

 case observed in Stentor where disintegration in the posterior 

 half of the body proceeded from the posterior end and the rare 

 cases in Paramcecium where a swelling appears over the posterior 

 vacuole only undoubtedly result from temporary stimulation of 

 the posterior regions. The dynamic gradient is not to be 

 conceived as fixed and invariable; it may be temporarily or in 

 many cases even permanently eliminated. But wherever it is 

 present to a certain degree and more or less continuously existent 

 it must determine both morphological and physiological differ- 

 ences along the axis. 



The facts of embryology indicate that a gradient in rate of 

 metabolism exists or arises early in the embryonic development 

 of every animal and that the region of highest rate becomes the 

 apical or cephalic region. In plants likewise the apical region 

 of the axis is undoubtedly the region of highest metabolic rate. 



Attention has already been called in earlier papers (Child, 'i3#, 

 'i3c) to these and to other facts and further data will be presented 

 in the future. The facts indicate as I believe that a gradient in 

 the rate of metabolism or of certain metabolic processes is the 

 dynamic basis of morphological and physiological polarity in 

 organisms. The existence of such a gradient in unicellular 

 organisms and the striking relation between its features and the 

 morphological and physiological features of the different species 

 in these as well as in multicellular forms is to say the least sug- 

 gestive. It points very clearly to a fundamental similarity 

 between unicellular and multicellular organization and differ- 

 entiation. 



These observations are also of some interest in another con- 

 nection. Loeb ('99) has advanced the hypothesis that the 

 nucleus is the chief organ of oxidation in the cell and has inter- 



