282 BIOLOGY OF THE PROTOZOA 



Resume. — In the preceding pages an hypothesis has been devel- 

 oped for the purpose of bringing together a large array of discon- 

 nected facts in one comprehensive biological generalization. The 

 underlying principle is the irritability of protoplasm as manifested 

 by the phenomena of adaptation. The fundamental organization 

 or particular type 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 chemi- 

 cal and physical reactions going on between and among the diverse 

 parts of the organization and between these and the environment. 

 Adaptation is the response of the organization to unusual condi- 

 tions. 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. Among 

 the latter are new combinations which occur with amphimixis. 

 Here, also, are the substances which are formed as a result of metab- 

 olism, particularly of oxidation. These may or may not be labile, 

 i. e., subject to reversal of phase in a physical sense, or to participa- 

 tion 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 com- 

 binations with other substances in the protoplasm are possible 

 and the results are manifested as differentiations. 



On this basis we interpret the differentiations which appear 

 with the intake of water and oxygen by an encysted organism 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 differentiations which are reduced or cast out 

 through protoplasmic activities at division, leaving the organization 

 in a labile state characteristic of the early inter-divisional period. 

 If the reorganizations effected by these divisional activities are 

 always the same generation after generation, then, on the hypoth- 

 esis, there is no a priori reason why under appropriate environ- 

 mental conditions, metabolic activities or vitality, should not 



