16 THE NATURE AND ORIGIN OF LIFE 



held in suspension in a fluid called a solvent ; often they 

 may be taken as minute spherules formed of a different fluid. 



Here, too, is a phenomenon of structure ; but it is of 

 dimensions quite different from those of the molecular or 

 chemical phenomenon ; each particle in suspension in a 

 colloid contains a very great number of molecules. 



Finally, a nebula in the heavens may be considered a 

 giant colloid ; but nebulae have no direct relation with 

 life, whereas molecules and true colloids, on the contrary, 

 very particularly concern the biologist. 



One of the first conquests of biology properly so called 

 was due to Dujardin, who asserted that all living beings 

 are formed of sarcode ; later, the word protoplasm was 

 substituted for sarcode, and its use has prevailed in science. 

 But it must be acknowledged that the unity of the word 

 protoplasm at first veiled an error ; it was believed that 

 protoplasm was the same in all living bodies, and so we had 

 only to say that all living bodies were of the same state 

 the protoplasmic state. 



The expression, also, was very vague. A few years ago, 

 if a biologist had been asked to define the protoplasmic 

 state an expression of which he made daily and copious 

 use he would have had to answer that a state is said to 

 be protoplasmic where we find substances living ; but that 

 there are many differences, even in mere look, between the 

 protoplasm of amoebae and that of bacteria. The word 

 protoplasm was, therefore, a synonym of " the particular 

 physical state of living substances " ; and Dujardin's discovery 

 amounted to this, w y hich was not without value : there is such 

 similarity of state among different living substances that, 

 from a structural point of view, we may bring them under 

 a single denomination. 



Recent science allows us to define more exactly that 



