126 M. Duinas on the Constitution of Milk and Blood. 



The siege of Paris will have proved tliat we have no pretension 

 to make bread or meat from their elements, and that we must 

 still leave to nurses the mission of producing milk. If some 

 illusions upon this point have found their way into the minds 

 of jjersons ill-informed as to the true state of science, they are 

 due to the dangerous play of words to which the expressions 

 organic ckemistry and organic substances lend themselves, 

 when applied as these are indifferently to definite compounds 

 such as alcohol or citric acid, which are unfitted for life, and to 

 indefinite tissues, the seat of life. 



The former (foreign to life, and true chemical species) are 

 the only ones that synthesis has reproduced. Tlie latter, 

 which can be formed only under the impulse of a living germ, 

 and which receive, preserve, and transfer the forces of life, are 

 not definite species ; the synthesis of the laboratories does not 

 reach them. The only synthesis which has hitherto been 

 observed in the case of the chemical materials which consti- 

 tute living tissues, is that determined in brute matter by the 

 presence and impulse of the living germ itself. 



All those chemical syntheses, otherwise so worthy of inter- 

 est, which have been indicated as reproducing organic matters, 

 have therefore in reality reproduced only matters unfitted for 

 life — that is to say, mineral matters. Thus, of every living 

 matter or matter that has lived, we must still, whether we 

 speak as chemists or as physiologists, say what was said of it 

 formerly : omne vivum ex ovo — that which is not life has 

 brought nothing to life. 



With regard to the constitution of milk, the phenomena 

 presented hy the clarifying of butter have been sometimes em- 

 ployed either to demonstrate or to dispute the existence of the 

 membranes which envelo})e the butyrous globules ; I cannot 

 at })resent regard these phenomena as having any value in this 

 res])ect. 



It has been said, for example, that the separation of butter 

 was the result of the formation of lactic acid arising from the 

 action of the air, favoured by churning. Numerous experi- 

 ments effected in my laboratoiy- ujion a practical scale, have 

 shown that butter separates equally promptly, and at least 

 equally abundantlv, from a milk to which a large amount of 

 bicarbonate of soda has been added, as from natural milk. 

 The alkaline reaction of the fonner, which is nuiintained 

 during the o])evation and after its completion, has no infiuence 

 either upon its duration or its result. The proportion of 

 butter, far from being diminished, seems even to have been 

 increased by it. 



The formation of lactic acid is tlicrct'orc not necessary for 



