STRUCTURE OF CELLS. 27 



substances which are obtained from cells after their death are pre- 

 existent in them during life, or are only the products of disin- 

 tegration. Hermann is of opinion that myosin is one of these 

 products of disintegration. Of the nature of the functions 

 fulfilled by the water and other inorganic compounds that 

 exist in protoplasm, we know absolutely nothing. 



2 STRUCTURE OF CELLS. Briicke* described a system of lacunae 

 in the salivary corpuscles, the cavities of which he thought 

 were occupied by an intracellular fluid. He stated that the 

 same appearances were presented by the protoplasm of the 

 vegetable cells composing the stinging hairs of the nettle. 

 Heidenhain-f- held the same opinion, and further maintained 

 that the intracellular fluid was moved by the protoplasm in 

 the same way that the contents of the intestines were pro- 

 pelled onwards by the peristaltic movements of the intestinal 

 walls. 



The protoplasm of vegetable cells may be so arranged that it tra- 

 verses the space within the cellulose wall like a spider's web, and in 

 such case the spaces between the protoplasmic fibres are occupied with 

 a fluid ; or the protoplasm may be reduced to a thin layer lining the 

 inner surface of the cellulose wall, the interior of which again is 

 bathed with fluid. But this cell fluid is not to be confounded with 

 that which occupies the inner spaces or lacunae of the protoplasm itself. 



It may be observed in the flask-shaped glands of the 

 nictitating membrane of the eye of the frog, that the size of the 

 gland cells undergoes considerable variation. Sometimes the 

 cells project so far into the lumen of the tube that this is re- 

 duced to an extremely small diameter ; whilst, on the other hand, 

 the cells are sometimes so contracted that the gland appears 

 like a bladder lined with a simple layer of epithelium. These 

 differences are not easy to comprehend, except on the suppo- 

 sition that the gland cells have by contracting expressed fluid 

 from their interior. 



It is also probable that at different times the protoplasm 



* Ueber die sogenannte Molecular bewegung. 

 t Studien des Physiologischen Instttuts zu Breslau, Heft u. 



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