METHODS 49 



That is, in the second member of this chemical equation 

 you find none of the chemically defined bodies which ap- 

 peared in the first member. C and D are always different 

 from A and B. 



On the contrary, in the example of bacteria, the sub- 

 stance of the original bacterium which effectively reacted, 

 since it gave the specific character to the reaction, is found, 

 and considerably increased at that, in the second member 

 of the chemical equation which represents the phenome- 

 non. 



To write symbolically this equation of a bacterium's 

 multiplication, we must observe that such multiplication 

 is made at the expense of certain nutritive substances which 

 have disappeared from the culture-medium during the 

 reaction ; these substances I represent by the letter Q. At 

 the same time that the bacteria multiply, there also appear 

 in the medium new substances which we may call substances 

 accessory to the assimilation, and which, always the same, 

 are produced whenever the same bacterial species multiplies 

 in the same conditions. I represent by the letter R these 

 accessory substances of assimilation. 



Now let a be the sum total of the active substances of the 

 bacteria, and suppose the reaction to stop when a number 

 of bacteria has been formed (this number X being so much the 

 greater as the reaction has continued longer, possibly equal 

 to two, to four, eight, sixteen and soon, but always greater 

 than one) : the chemical equation representing the pro- 

 duction of these new bacteria will be in accordance with the 

 law of the conservation of matter : 



a + Q =*a -f-R 



I call this the chemical equation of elementary life as mani- 

 fested. I wrote out this equation for the first time ten 



4 



