VITALITY 505 



such instances, particularly if the differentiations are manifested by 

 structural features whereby one type can be distinguished from 

 the other we are justified in using the term sex in the same sense as 

 used for Metazoa. 



Summary.— In the preceding pages an hypothesis has been 

 de\'eloped for the purpose of bringing together a large array of 

 disconnected facts in one comprehensive biological generalization. 

 The underlying principle is the irritability of protoplasm as mani- 

 fested by the phenomena of adaptation. The fundamental organ- 

 ization or particular t}j>e and arrangement of the proteins, 

 carbohydrates, salts, and other constituents of living substance, is 

 specific for each kind of organism. Vitality is interpreted as the 

 aggregate of chemical and physical reactions going on between and 

 amongst the diverse parts of the organization and between these and 

 the environment. Adaptation is the response of the organization to 

 unusual conditions. It involves somewhat changed reactions and 

 these in turn, may involve new substances which may or may not be 

 the basis of new morphological elements, but the fundamental 

 organization becomes at least somewhat modified. The inciting 

 causes of such changes may be of environmental or of internal 

 origin. Amongst the latter are new combinations which occur with 

 amphimixis. Here also, are the new^ substances which are formed 

 as a result of metabolism, particularly of oxidation. These may 

 or may not be labile, i. e., subject to reversal of phase in a physical 

 sense, or to participation in the vortex of vital activities generally. 

 If not labile they become metaplastids and may or may not serve 

 some useful purpose for the organism. If such products of activity 

 are labile new combinations with other substances in the protojjlasm 

 are possible and the results are manifested as difterentiations. 



On this basis we interpret the differentiations which appear with 

 the intake of water and oxygen by an encysted organism (p. 489) 

 or the various activities characteristic of Protozoa during the early 

 phases of the life history. On the basis of changes due to general 

 metabolic activities and due to the specific organization of any 

 particular form, we interpret the drastic alterations which accom- 

 pany and characterize cell division. These involve the changes in 

 physical condition of the various colloidal substances, such for 

 example, as the increase in permeability due possibly to the accumu- 

 lation of hydrogen ions, and the absorption of water. They also 

 involve cytolytic activities as indicated by the disintegration and 

 absorption of kinetic elements, of eliminated nuclear chromatin, 

 and division of all the substances active in vitality. The conditions 

 under which these divisional activities are manifested represent 

 inter-divisional difterentiations w^hich are reduced through proto- 

 plasmic activities at division leaving the organization in a labile 



