September 6, 1912] 



SCIENCE 



299 



already mentioned, Avhich are also of a 

 colloid nature but of simpler constitu- 

 tion than itself, and which differ from 

 the catalytic agents employed by the 

 chemist in the fact that they produce their 

 effects at a relatively low temperature. In 

 the course of evolution special enzymes 

 would become developed for adaptation to 

 special conditions of life, and with the ap- 

 pearance of these and other modifications, 

 a process of differentiation of primitive 

 living matter into individuals with definite 

 specific characters gradually became estab- 

 lished. We can conceive of the production 

 in this way from originally undifferentiated 

 living substance of simple differentiated 

 organisms comparable to the lowest forms 

 of protista. But how long it may have 

 taken to arrive at this stage we have no 

 means of ascertaining. To judge from the 

 evidence afforded by the evolution of higher 

 organisms it would seem that a vast period 

 of time would be necessary for even this 

 amount of organization to establish itself. 



The next important phase in the process 

 of evolution would be the segregation and 

 moulding of the diffused or irregularly 

 aggregated nuclear matter into a definite 

 nucleus around which all the chemical 

 activity of the organism will in future be 

 centered. Whether this change were due 

 to a slow and gradual process of segrega- 

 tion or of the nature of a jump, such as 

 nature does occasionally make, the result 

 would be the advancement of the living 

 organism to the condition of a complete 

 nucleated cell : a material advance not only 

 in organization but — still more important 

 — in potentiality for future development. 

 Life is now embodied in the cell, and every 

 living being evolved from this will itself be 

 either a cell or a cell-aggregate. Omnis 

 cellula e cellula. 



After the appearance of a nucleus — but 

 how long after it is impossible to conjecture 



— another phenomenon appeared upon the 

 scene in the occasional exchange of nuclear 

 substance between cells. In this manner 

 became established the process of sexual 

 reproduction. Such exchange in the uni- 

 cellular protista might and may occur be- 

 tween any two cells forming the species, 

 but in the multicellular metazoa it became 

 — like other functions — specialized in par- 

 ticular cells. The result of the exchange is 

 rejuvenescence; associated with an in- 

 creased tendency to subdivide and to pro- 

 duce new individuals. This is due to the 

 introduction of a stimulating or catalytic 

 chemical agent into the cell which is to be 

 rejuvenated, as is proved by the experi- 

 ments of Loeb already alluded to. It is 

 true that the chemical material introduced 

 into the germ-cell in the ordinary process 

 of its fertilization by the sperm-cell is 

 usually accompanied by the introduction of 

 definite morphological elements which 

 blend with others already contained within 

 the germ-cell, and it is believed that the 

 transmission of such morphological ele- 

 ments of the parental nuclei is related to 

 the transmission of parental qualities. But 

 we must not be blind to the possibility that 

 these transmitted qualities may be con- 

 nected with specific chemical characters of 

 the transmitted elements ; in other words, 

 that heredity also is one of the questions 

 the eventual solution of which we must 

 look to the chemist to provide. 



So far we have been chiefly considering 

 life as it is found in the simplest forms of 

 living substance, organisms for the most 

 part entirely microscopic and neither dis- 

 tinctively animal nor vegetable, which were 

 grouped together by Haeckel as a separate 

 kingdom of animated nature — that of pro- 

 tista. But persons unfamilar with the 

 microscope are not in the habit of asso- 

 ciating the term "life" with microscopic 

 organisms, whether these take the form of 



