236 THE ORIGIN AND PROPAGATION OF DISEASE. 



ciiic characters of the globules of yeast ; he only determined the bare 

 fact of their existence. 



But in 1837 the French chemist Cagniard-Latour* examined the yeast- 

 globules with more care. He measured their size, and found them to be 

 at most 25^0 o^ ^^ ™*^^ ^^ diameter. He declared that thej' were of a 

 vegetable nature, and that they multiplied by the j)rocess of budding. 

 He called attention to the fact that during the fermentation of beer the 

 ferment increases in quantity, producing at the end of the process six 

 or seven times as much yeast as was introduced at the beginning; and 

 he first broached the idea that " it is probably by some effect of their 

 vegetation that the yeast-globules destroy the equilibrium of the ele- 

 ments of the sugar." 



The theory, however, was at that time premature, audit did not meet 

 with general acceptance. The existence of the yeast-plant, so far as 

 then known, was an isolated fact, confined to the single case of ferment- 

 ing beer. The opposite theory, of the catalytic action of an albuminous 

 liquid, was maintained by Liebig with all the force of his remarkable 

 genius, and was consequently almost universally adopted. The yeast- 

 plant was thought to be an incidental growth in the fermenting fluid, 

 and not to have any direct or important connection with the process 

 itself. 



About fifteen years ago a new epoch was inaugurated in the history 

 of fermentation by the brilliant researches of Pasteur. The existence 

 and growth of a fungoid vegetation were now found not to be confined 

 to the single case of beer-yeast, but to be a general fact common to the 

 alcoholic fermentation of beer, wine, and bread, and also to a variety of 

 other kinds, such as the viscous, butyric, and acetic fermentations. The 

 fungus itself was industriously studied in its different genera and spe- 

 cies, with their si^ecific modes of growth and reproduction, like those of 

 any other natural family of plants; so that the Saccharomyces cerevisice, 

 or the yeast-fungus of beer, can now be distinguished from the other spe- 

 cies of alcoholic ferments, as well as from the fungi of other kinds of 

 fermentation. 



The different view thus introduced is most distinctly exxDressed by 

 Pasteur himself. "According to the old theory," he says, " fermenta- 

 tion is a process correlative with death, and depends on the decay of 

 albuminous matter; according to the new one, it is correlative with life, 

 that is, the active growth and development of the fungous vegetation. * * 

 The yeast-globules are actual living vegetable cells, capable of producing 

 the transformation of sugar, just as the cells of the mammary gland in a 

 living animal transform the ingredients of the blood into the ingredients 

 of the milk." 



The discussions on this subject, which lasted for ten years, took a 

 very wide range, and especially became connected with the kindred 

 topic of " spontaneous generation." The experiments of Pasteur and 

 * " Annales de Chimie et cle Physique," 1838, tome Isviii, p. 216. 



