198 THEORY OF THE CELLS. 
as an instance of this. A decoction of malt will remain for 
a long time unchanged; but as soon as some yeast is added 
to it, which consists partly of entire fungi and partly of a 
number of single cells, the chemical change immediately ensues. 
Here the decoction of malt is the cytoblastema; the cells clearly 
exhibit activity, the cytoblastema, in this instance even a boiled 
fluid, being quite passive during the change. The same occurs 
when any simple cells, as the spores of the lower plants, are 
sown in boiled substances. 
In the cells themselves again, it appears to be the solid 
parts, the cell-membrane and the nucleus, which produce the 
change. The contents of the cell undergo similar and even 
more various changes than the external cytoblastema, and it is 
at least probable that these changes originate with the solid 
parts composing the cells, especially the cell-membrane, because 
the secondary deposits are formed on the inner surface of the 
cell-membrane, and other precipitates are generally formed in 
the first instance around the nucleus. It may therefore, on the 
whole, be said that the solid component particles of the cells 
possess the power of chemically altering the substances in con- 
tact with them. 
The substances which result from the transformation of the 
process itself, a phenomenon which is met with only in living organisms. Neither do 
{ see how any further proof can possibly be obtained otherwise than by chemical ana- 
lysis, unless it can be proved that the carbonic acid and alcohol are formed only at 
the surface of the fungi. I have made a number of attempts to prove this, but they 
have not as yet completely answered the purpose. A long test-tube was filled with 
a weak solution of sugar, coloured of a delicate blue with litmus, and a very small 
quantity of yeast was added to it, so that fermentation might not begin until several 
hours afterwards, and the fungi, haying thus previously settled at the bottom, the fluid 
might become clear. When the carbonic acid (which remained in solution) commenced 
to be formed, the reddening of the blue fluid actually began at the bottom of the tube. 
If at the beginning a rod were put into the tube, so that the fungi might settle upon 
it also, the reddening began both at the bottom, and upon the rod. This proves, 
at least, that an undissolved substance which is heavier than water gives rise to 
fermentation ; and the experiment was next repeated on a small scale under the 
microscope, to see whether the reddening really proceeded from the fungi, but the 
colour was too pale to be distinguished, and when the fluid was coloured more 
deeply no fermentation ensued; meanwhile, it is probable that a reagent upon car- 
bonic acid may be found which will serve for microscopic observation, and not 
interrupt fermentation. The foregoing inquiry into the process by which organized 
bodies are formed, may perhaps, however, serve in some measure to recommend this 
theory of fermentation to the attention of chemists. 
