LIFE: ITS NATURE, ORIGIN AND MAINTENANCE 21 



matter into a definite nucleus around which all the chemical activity 

 of the organism will in future be centred. Whether this change were 



due to a slow and gradual process of segregation or 



of the nature of a J um P' such as Nature does occa- 

 sionally 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 organisation 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. Oinnis cellula e celluld. 



After the appearance of a nucleus but how long after it is impossible 

 to conjecture another phenomenon appeared upon the scene in the occa- 

 sional exchange of nuclear substance between cells. 



se^Sfferences. In this manner became established the process of 



sexual reproduction. Such exchange in the unicellular 

 organism might and may occur between any two cells forming the species, 

 but in the multicellular organism it became like other f unctions - 

 specialised in particular cells. The result of the exchange is rejuvene- 

 scence ; associated with an increased 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 experiments of 'Loeb already alluded to. It is true that the 

 chemical material introduced into the germ-cell in the ordinary process of 

 its fertilisation by the sperm-cell is usually accompanied by the introduc- 

 tion of definite morphological elements which blend with others already 

 contained within the germ-cell, and it is believed that the transmission of 

 such morphological elements of the parental nuclei is related to the trans- 

 mission of parental qualities. But we must not be blind to the possibility 

 that those transmitted qualities may be connected 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 formsof living substance, organisms for the most part entirely micro- 

 scopic and neither distinctively animal nor vegetable, 

 Aggregate life. which have sometimes been grouped together as a sepa- 



rate kingdom of animated nature that of Protista. But 

 persons unfamiliar with the microscope are not in the habit of associating 

 the term ' life ' with microscopic organisms, whether these take the form 

 of cells or of minute portions of living substance which have not yet 

 attained to that dignity. We most of us speak and think of life as it 

 occurs in ourselves and other animals with which we are familiar ; and as 

 we find it in the plants around us. We recognise it in these by the 

 possession of certain properties movement, nutrition, growth, and repro- 

 duction. We are not aware by intuition, nor can we ascertain without the 



