OTHER THEORIES OF SPECIES-FORMING. 225 



which results in conducting each cell to exactly that place which 

 it ought to occupy. 



In addition to the theories of an ultimate micromeric structure 

 of protoplasm, certain other recent hypothetical explanations of 



Verworn's bio- the special properties of protoplasm should be noted, 

 gen hypothesis. One is the biogen hypothesis of Verworn, the physiol- 

 ogist of Gottingen. one the chemism theory of Le. Dantec, one 

 the physical machine theory of Delage, and another is the general 

 vital principle hypothesis of the neo-Vitalists. Verworn's hypoth- 

 esis to account for the physiological activities of protoplasm, i. e., 

 the special life attributes, as assimilation, disassimilation, growth, 

 irritability, etc., consists in the postulation of a complex chemical 

 compound of unknown structure called biogen, but with the special 

 capacities of an enzyme. This biogen is assumed to be constantly 

 labile, i. e., breaking down and rebuilding itself and by this per- 

 formance acting as a go-between (enzyme or perhaps katalysator) 

 between the atmospheric oxygen brought to the cell by the blood 

 and the oxidisable (food) products (also brought by the blood). 

 Not only can the biogen rebuild itself, but by polymerisation it can 

 grow, that is, increase the size of its molecules by adding side- 

 chains of atoms. This, according to Verworn, constitutes cell 

 growth. This growth is not indefinite, as the atoms tend to break 

 away again and thus there is a limit to the size of the biogen mole- 

 cules. The author only presents his conception of biogen as a good 

 working hypothesis. 



Delage has also offered a tentative physico-chemical explanation 

 of certain of the properties of protoplasm, as its movements, its 



Delage's ma- nutrition, and even its reducing division, on the basis 

 chine theory. of osmotic effects due to the constant interchange of 

 substance from the outer layers of the cell protoplasm to the inner 

 through fine membranes or special protoplasmic layers which he 

 assumes to enclose each cell part, i. e., nucleus, chromosomes, etc. 

 Nutrition, for example, is effected according to Delage, by constant 

 selective osmotic exchanges between the liquid and semi-liquid 

 parts of the cell, the blood-plasm of course constantly bringing 

 food and carrying off excreta to and from the periphery of each 

 cell. Cell division is the result of mutual pulls and pushes, its 

 essential feature always being the actual sundering of parts ; but 

 how this mechanical process is guided or controlled as it is, or even 

 initiated, is left unexplained. 



Le Dantec holds that life is a chemical phenomenon. ''La vie est 



Le Dantec's the- un phenomene chimique, c'est-a-dire que les seuls 

 ory of chemism. caracteres essentiels par lesquels une action vitale 

 differe d'une manifestation de 1'activite de la matiere brute sont rela- 



