656 THE MICROSCOPE. 



"wliicli lie at one time declared to be unicellular animals 

 with a contractile cell-membrane and contents. The con- 

 tractile substance is characterised by the following attri- 

 butes : it is homogeneous, or finely granular, transparent, 

 of the consistence of albumen, gelatiniform, soft, more 

 refractive than water, but less so than oil ; insoluble in 

 water, but gradually decomposed ; destroyed by caustic 

 potash ; coagulated and contracted by carbonate of j^otash, 

 as well as by alcohol and nitric acid ; having the power of 

 forming aqueous cavities, which originate either by the 

 separation of the water contained in it, or by its reception 

 from without ; owing to which the remainder becomes 

 denser and more granular, and lastly, it represents the 

 appearance, in water, of contractile drops, which move like 

 an Amcjeba. All these properties had already been observed 

 by Dujardin, in a substance of which the Infusoria and 

 Rhizopoda are principally composed, and which he termed 

 " sarcode ; " the aqueous spaces or hollows he named 

 "vacuoles," regarding them as the most characteristic 

 features of the substance ; these spaces had been errone- 

 ously regarded by Ehrenberg as stomachs. All these 

 properties, however, are possessed by a substance in the 

 plant-cell, which must be regarded as the prime seat of 

 almost all vital activity, but especially of all the motile 

 phenomena in its interior — the protoplasm. !N'ot only do 

 its optical, chemical, and physical relations coincide with 

 those of the " sarcode," or contractile substance, but it 

 also possesses the faculty of forming "vacuoles" at all 

 times, and even externally to the cell ; a property, it is 

 true, which has for the most part been hitherto overlooked 

 or misinterpreted. These clear, aqueous spaces, the so- 

 termed vesicular contents, aie present in all young 

 cells, and play a considerable part in cell-division, and the 

 sap-currents ; they are in all resj^ects analogous to the 

 vacuoles of the sarcode.^ 



(1) Mr Tluxlcy has satisHod himself that in all the animal tissues the so- 

 called nucleus (endoplast) is the homoloyue of the primordial utricle, with 

 nucleus and contents (endoplast) of the i)lant, the other histological elements 

 being invariahly modifications of the ])eri])lasti(' substance. Ui)on this view we 

 lind that all the disia-ejiancies wliich had a]ii)eared to exist between the aniiual 

 and vegetable structiu'C disappear : and it beconu's easy to trace the absolute 

 identity of i)\iin in the two, the dillerences between them being inoduced merely 

 by the nature and form of the deposits in, or modifications of, the periplastic 



