256 CLASSICS OF MODERN SCIENCE 

 it. We may mention vinous fermentation 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 con- 

 tents of the cell undergo similar and even more various changes than 

 the external the 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 

 contact with them. 



The substances which result from the transformation of the con- 

 tents of the cell are dififerent from those which are produced by change 

 in the external cytoblastema. What is the cause of this difference, if 

 the metamorphosing power of the cell-membrane be limited to its im- 

 mediate neighbourhood merely? Might we not much rather expect 

 that converted substance would be found without distinction on the 

 inner as on the outer surface of the cell-membrane? It might be 

 said that the cell-membrane converts the substance in contact with it 

 without distinction, and that the variety in the products of this conver- 

 sion depends only upon a difference between the convertible substance 

 contained in the cell and the external cytoblastema. But the question 

 then arises, as to how it happens that the contents of the cell differ 

 from the external cytoblastema. If it be true that the cell- 

 membrane, which at first closely surrounds the nucleus, expands in the 

 course of its growth, so as to leave an interspace between it and the 

 cell, and that the contents of the cell consist of fluid which has entered 

 this space merely by imbibition, they cannot differ essentially from the 

 external cytoblastema. I think therefore that, in order to explain the 



