PROTOPHYTIO AND OTHER FUNGI. 315 



mg beer is capable of propagating its fermentation to fresh wort. 1 A 

 most notable instance of such propagation is afforded by the spread of 

 the disease termed ' pebrine ' among the Silkworms of the south of 

 France; the mortality caused by it being estimated to produce a money- 

 loss of from three to four millions sterling annually, for several years 

 following 1853, when it first broke out with violence. It has been shown 

 by microscopic investigation, that in silkworms strongly affected with 

 this disease, every tissue and organ in the body is swarming with minute 

 cylindrical corpuscles about 1-6, 000th of an inch long; and that these 

 even pass into the undeveloped eggs of the female moth, so that the dis- 

 ease is hereditarily transmitted. And it has been further ascertained by 

 the researches of Pasteur, that these corpuscles are the active agents in 

 the production of the disease, which is engendered in healthy silkworms 

 by their reception into their bodies; whilst, if due precautions be taken 

 against their transmission, the malady may be completely exterminated. 

 311. Nearly allied to the Scliizomycetes in the simplicity of its charac- 

 ter and in its ' zymotic ' action, is the Saccharomyces ( Torula) cerevisice; 

 the presence of which in Yeast gives to it the power of exciting the alco- 

 holic fermentation in saccharine liquids. When a small drop of yeast is 

 placed under a magnifying power of 400 or 500 diameters, it is seen to 

 contain a large number of globular or ovoid cells, averaging about 

 1-3, 000th of an inch in diameter, for the most part isolated, but some- 



I-TG. IDS. 



Torula cerivisice, or Yeast-plant, as developed during the process of fermentation: a, 6, c, d, 

 successive stages of cell-multiplication. 



times connected in short series; and each cell is filled with a nearly color- 

 less ( endoplasm,' usually exhibiting one or more vacuoles, but never 

 showing a nucleus. When placed in a fermentible fluid containing some 

 form of nitrogenous matter in addition to sugar, 3 they vegetate, in the 

 manner represented in Fig. 198. Each cell puts forth one or two projec- 

 tions, which seem to be young cells developed as buds or offsets from their 

 predecessors; these, in the course of a short time, become complete cells, 

 and again perform the same process; and in this manner the single cells 

 of yeast develop themselves, in the course of a few hours, into rows of 

 four, five, or six, which remain in continuity with each other whilst the 

 plant is still growing, but which separate if the fermenting process be 

 checked, and return to the isolated condition of those which originally 

 constituted the yeast. Thus it is that the quantity of yeast first intro- 



1 See Prof. Burden Sanderson 'On the Intimate Pathology of Contagion' in 

 the Privy Council " Reports on the Public Health " for 1870 



2 It appears from the researches of Pasteur, that although the presence of Al- 

 buminous matter (such as is contained in a saccharine wort, or in the 3Uices of 

 fruits) favors the growth and reproduction of Yeast, yet that it can live and mul- 

 ply in a solution of pure Sugar, containing ammonium-tartrate with small quan- 

 tities of Mineral salts; the decomposition of the ammonia-salt affording it the ni- 

 trogen it requires for the production of protoplasm, while the sugar and water 

 supply the carbon, oxygen, and hydrogen. 



