Special Morphology and Classification. 277 
propagates itself on vinegar, it a aaa it into carbon 
dioxide and water. : 
[ Zorula or Saccharomyces Cereviste being one of the 
types of vegetable life to which special attention 1s called in 
the syllabus of the University of London, the following is 
given as an epitome of our present state of knowledge con- 
cerning it, according to Professor Huxley. Yeast is the 
brownish fluid which possesses the property of causing in any 
solution which contains sugar the change known as /ermenta- 
tion, that is, the conversion of the sugar into alcohol, which 
remains in the fluid, and carbon dioxide (carbonic acid gas), 
which is given off in the form of bubbles. Yeast, when | 
evaporated at a low temperature, 1s reduced to a powdery 
mass which retains for a considerable period its property of 
fermenting saccharine fluids. Fermentation is prevented by 
boiling either the yeast or the saccharine fluid, or by pre- 
viously straining the yeast through a very fine filter, such as_ 
porous earthenware ; nor does any change take place if, 
after boiling the fluid, it.is allowed to come into contact 
only with air which has been passed through cotton-wool. 
Hence it is concluded that the fermentation is caused by a 
solid substance contained in the yeast, which cannot pass 
through the earthenware or cotton-wool ; and if yeast 1s 
examined under a low magnifying power, it is found to con- 
tain a number of nearly spherical transparent granules, 
averaging about ‘ooo3 of an inch in diameter, each of which 
is a Zorufa. "ach individual is an ordinary vegetable cell, 
usually containing a vacuole, but never a nucleus ; and the 
cells are either solitary or associated in heaps or strings. On 
analysis it is found to consist of carbon, hydrogen, oxygen, 
nitrogen, sulphur, phosphorus, potassium, magnesium, and 
calcium ; the last four in very small quantities. Its chief 
proximate constituents are (1) a protein-compound analo- 
gous to casein ; (2) cellulose ; (3) fat or oil ; (4) water ; the 
larger part of the mineral substances being contained in the 
procoplasm. The Zorula is the sole cause of fermentation 
