76 Fermentation and Kindred Phenomena. 



a perfectly definite manner, which we may represent by what 

 is called a chemical equation, thus : — 



C 6 H 12 O e = 2 C0 2 + 2 C 2 H 8 O * 



Grape Sugar. Carbonic Acid. Spirit or Alcohol. 



What has caused this change in the sugar ? It must be 

 apparent to you, I think, that it is the yeast (for nothing was 

 present but the two things, and it can easily be proved that 

 sugar will not ferment without the yeast). Then comes the 

 question, and it is the very essence of the whole matter — What 

 is the nature of the influence which the yeast exercises ? 



Loewenhoeck was the first to examine yeast under the 

 microscope in 1680, and to find that it consists of very minute 

 globules. Cagniard de Latour in the present century took up 

 Loewenhoeck's work, which had almost been forgotten. " He 

 observed that yeast consists of a mass of organic globules sus- 

 ceptible of reproducing themselves by means of buds which 

 appeared to belong to the vegetable kingdom, and not to be 

 simply organic or chemical matter, as supposed. He concluded 

 that it is very probably by some effect of their vegetation that 

 the globules of yeast disengage carbonic acid from the saccharine 

 liquid and convert it into spirit." 



The great German chemist Liebig took, however, a totally 

 different view of the matter — a view which he can scarcely be 

 said to have originated, as his ideas were almost identical with 

 those of Willis and Stahl, chemists of the 17th century. His 

 theory was as follows : — Yeast, and in general all animal and 

 vegetable matters in a state of putrefaction, will communicate 

 to other bodies the condition of decomposition in which they 

 are themselves placed. The motion which is given to their own 



* The chemist employs a kind of shorthand to represent the composition of substances 

 and their decompositions and reactions. The " equation" in question indicates, first, 

 the composition of the "molecule" or smallest particle of grape sugar capable of exis- 

 tence — the small indices showing how many atoms of the different elements it is 

 composed of are present : " C 6 " representing six atoms of carbon, " H 12 " twelve atoms 

 of hydrogen, "O e " six atoms of oxygen. It also shows that the molecule of sugar is 

 decomposed into two molecules of carbonic acid (each containing one atom of carbon 

 and two atoms of oxygen) and two molecules of spirit (each containing two atoms of 

 carbon, six of hydrogen, and one of oxygen). The term "equation" is employed 

 because the number of atoms on each side of the = sign is the same. 



