THE VITAL PROPERTIES OF THE CELL 149 



membered that a large proportion of plant cells, namely all those 

 which do not contain chlorophyll, ai*e in a position similar to that 

 occupied by animal cells; these also, since they cannot assimi- 

 late directly, must obtain from the green cells, the material neces- 

 sary for the maintenance of their life, for their growth, and for 

 their reproduction. Thus the same antithesis, which is present 

 in the economy of nature between plants and animals, also exists 

 in the plant itself between its colourless and its chlorophyll-con- 

 taining cells. 



Claude Bernard has shortly and in a striking way expressed the 

 relationship in the following words : 



" If, in the language of a mechanician, the vital phenomena, 

 namely the construction and destruction of organic substance, 

 may be compared to the rise and fall of a weight, then we may 

 say that the rise and fall are accomplished in all cells both plant 

 and animal, but with this difference, that the animal element 

 finds its weight already raised up to a certain level (niveau), and 

 that hence it has to be raised less than it subsequently falls. The 

 reverse occurs in the green plant cells. In a woi-d, ' Des deux 

 versants, celui de la descente est preponderant chez 1'animal ; 

 celui de la montee, chez le vegetal ' " (Claude Bernard, IV. la, 

 vol. ii. p. 514). 



Now, having placed the subject of the chlorophyll function in 

 its true position, we will proceed to examine the important 

 uniformity which exists in the chemistry of metabolism between 

 plant and animal cells. 



We must first lay stress upon the fact that a large number of 

 the materials made use of in progressive and retrogressive meta- 

 morphosis are common to both plants and animals. 



Further, the means by which certain important processes in 

 plant and animal cells are carried out appear to be similar. 

 Carbo-hydrates, fats and albuminous substances are not adapted 

 in every condition for direct use in the laboratory of the cell and 

 for conversion into other chemical compounds. It is necessary 

 to prepare them by transforming them into a soluble and easily 

 diffusible form. This occurs, for instance, when starch and glyco- 

 gen are converted into grape sugar, dextrose and levulose ; when 

 fat is split up into glycerine and fatty acids, or when proteids are 

 peptonised. 



Sachs (IV. 32a) describes the above-mentioned modifications of 

 carbo-hydrates, fats and proteids as their active condition, in dis- 



