26 PASTEUR AND AFTER PASTEUR 



the formation of zymaze may be stated in terms of 

 plant physiology : thus, the old lines of dispute are 

 left behind. 



Again, a wonderful advance was made, in 1879, 

 by Hansen's method of marking-down, in a thin 

 film of a very dilute mixture of yeast and water, 

 under the microscope, single cells, and then, when 

 these cells began to form colonies visible to the 

 unaided eye, making cultures from these colonies, 

 and thus obtaining a yeast of absolute purity and 

 of known pedigree. It seems that honours are 

 even between Pasteur and Hansen : from 1880, it 

 is Hansen ; before Hansen, it is Pasteur. 



Only, to him, vast industries presented them- 

 selves chiefly as hunting-grounds of science : they 

 were "parts of one stupendous whole": he was at 

 work not only to improve the world's beverages 

 though he was glad to do that, for the honour and 

 glory of France but to prove that all processes of 

 fermentation, decomposition, and putrefaction, are 

 infective processes : that they are due, not to the 

 oxygen in the air, but to the living dust in the air : 

 that they are an act of life, and cannot begin apart 

 from life. It is life which brings about these 

 chemical changes : and, in the absence of life, they 

 do not take place. These microscopic points of 

 life, these yeasts and bacteria, millions of them in 

 a drop or two of fermenting grape-juice, sour milk, 



