ON THE STRUCTURE OF CELLS 145 



others which were not previously visible. The 

 structure which has been observed has been gener- 

 ally supposed to consist of a " network of threads 

 embedded in a homogeneous substance." But this 

 so-called substance might itself be seen to consist 

 of a highly complicated structure if the sensitive- 

 ness and acuteness of our vision were greater 

 than they are. Btitschli regarded it as made up 

 of finely divided structures. 



When small drops of a mixture of finely powdered 

 potash and oil placed in water are observed, an 

 emulsion is formed which has the structure of the 

 foam-cells described by Quincke, and very possibly 

 to some extent of the nature of the liquid crystals 

 described by Lehmann. Such structures, however, 

 have what are called vacuoles or internal spaces 

 filled with liquid, as distinct from the outer and 

 more solid-like substance which corresponds to the 

 cytoplasm ; the vacuole corresponds to the centro- 

 some. The structure of living protoplasm, as in- 

 vestigated by the method of staining, is naturally 

 viewed with considerable doubt by many students of 

 the subject. 



Again the element phosphorus enters largely into 

 the compounds of which the nucleus is made up, 

 chiefly in the substance called nuclein, and it doubt- 

 less plays an important part in the process of meta- 

 bolism ; for phosphorus is highly phosphorescent, and, 

 as will be shown, this phenomenon appears to be 

 due to the simplest types of metabolism, resulting 

 from the building up and breaking down of molecules : 



