CHAPTER XV 



ANALYSIS BY MEANS OF REAGENTS OF THE SAME 

 DIMENSION AS LIFE 



WE will not start with the most general problem. That 

 would consist in the study of the consequences to a living 

 being of any variation whatsoever set up in the conditions of 

 its life. We must begin by limiting ourselves to some very 

 particular case in which the variation shows itself in a definite 

 body carrying its own properties along with it just as chemi- 

 cal reagents do. We bring together an animal and a given 

 reagent and, since all other conditions remain the same, 

 we shall be able to assign to the reagent used and to this 

 reagent alone the modifications we observe. 



When we have a living being very low in organization, 

 for example a unicellular being, we content ourselves with 

 adding the given reagent to the liquid in which the being 

 lives. I have already referred to an experiment of this 

 kind : it consisted in adding a small quantity of phenic 

 acid to the bouillon in which anthrax bacteridia were culti- 

 vated. But we estimated the result only by our first and 

 artificial method of analysis ; we verified that there was 

 a variation with reference to a reagent other than 

 phenic acid the variation which we called attenuation of 

 virulence. Such a result is not of general order ; it is only 

 the expression of a particular fact. 



When we have a living being of high organization such as 



