62 INDIVIDUALITY IN ORGANISMS 



staining the plants with neutral red and then killing 

 with cyanide or some other reagent the susceptibility 

 gradient can be made visible, for as the cells die the 

 red of the stain at first becomes deeper because of in- 

 creasing acidity, then changes to yellow as the alkali of 

 the solution enters, and finally all color disappears. 



FURTHER PHYSIOLOGICAL EVIDENCE FOR THE EXISTENCE 

 OF METABOLIC GRADIENTS 



The susceptibiHty gradients do not constitute the 

 only experimental evidence for the existence of meta- 

 bolic gradients in the organism. Estimations of carbon- 

 dioxide production by means of the Tashiro biometer,^ 

 which were made by Dr. Tashiro at my request, have 

 confirmed the results obtained by the susceptibiHty 

 method in all cases subjected to this test. The gradient 

 in carbon-dioxide production is similar to the gradient 

 in metabolic rate indicated by the differences in sus- 

 ceptibiHty. On the other hand, in the case of certain 

 nerves I have been able to confirm Tashiro 's recent 

 discovery of a gradient in carbon-dioxide production in 

 the direction of conduction of the impulse along the 

 fiber by the demonstration of a gradient in susceptibiHty 

 in the same direction, and have found a similar sus- 

 ceptibility gradient in certain other nerves for which 

 carbon-dioxide production has not been determined. 

 The gradient in the production of carbon dioxide indi- 

 cates the existence of a gradient in the rate or intensity 

 of the respiratory processes, the oxidations, the region 



^ Tashiro, "A New Method and Apparatus for the Estimation of 

 Exceedingly Minute Quantities of Carbon Dioxide," Am. Jour, of 

 Physiol., XXXII, 1913. 



