8 FOUNDATIONS Ci~ BIOLOGY 



to a common denominator was the final justification of the 

 prevision of the earlier workers in recognizing a life-science 

 biology. 



Although we speak of a common ' physical basis of life/ it 

 is of paramount importance to bear in mind that the proto- 

 plasm of no two animals or plants or, indeed, of different 

 parts of the same animal or plant is exactly the same. 

 Identity of protoplasm would mean identity of structure 

 and function identity of life itself. The concept proto- 

 plasm merely emphasizes that, after allowances are made 

 for all the variations, we still have the similarities far 

 outnumbering the dissimilarities in the 'agent of vital 

 manifestations.' 



The physical chemists tell us that matter in the living 

 state represents a type of COLLOIDAL CONDITION of matter 

 known as an emulsoid which, in turn, may exist either as a 

 sol the apparently homogeneous liquid state of living 

 matter; or as a gel the apparently amorphous semi-solid 

 state. Protoplasmic sols appear, as a rule, homogeneous be- 

 cause of the exceedingly small size of the molecular aggre- 

 gates which form them, while protoplasmic gels reveal either 

 a homogeneous or heterogeneous molar structure because of 

 the relatively large particles which set to form the gel. In 

 other words, living matter holds an intermediate position 

 between true solids and true liquids, and has many properties 

 of both, as well as many peculiar to itself. 



But this leaves the reader without any clear conception 

 of the appearance of protoplasm. As a matter of fact it is 

 as difficult to describe the appearance of, as it is to define, 

 protoplasm. It must be seen under the microscope to be 

 appreciated. With a moderate magnification, protoplasm 

 presents a fairly characteristic picture, appearing like a 

 translucent, colorless, viscid fluid containing many minute 



