i] FIXATION 9 



which it had been intimately mixed, and that the form 

 taken by the solid depends on the strength of the original 

 solution and on ,the nature both of the colloid substance and 

 of the fixative. If the solution is weak, when it coagulates 

 the solid takes the form of granules ; when it is stronger, it 

 may form either a network or a foam-structure according 

 to whether the coagulum is soluble or insoluble. For ex- 

 ample, a gelatin solution coagulated with sublimate forms 

 a soluble coagulum which has an alveolar structure, while 

 albumen treated with sublimate, or gelatin with formalin, 

 forms an insoluble coagulum which is reticular in structure. 

 HARDY further found that if fine particles are suspended in 

 the solution, they come to lie at the nodes of the mesh- or 

 foam-work when the solution is coagulated, and that the 

 size of the particles determines the fineness or coarseness 

 of the meshes. Applying these observations to cell-struc- 

 tures, he suggests that the mesh-work commonly found in 

 fixed nuclei is due simply to the effects of fixation, and 

 that the size of the meshes depends on the fineness of 

 division of the chromatin particles in the nucleus. Under 

 some circumstances he was able to fix nuclei with no mesh- 

 work at all, but merely with granules of chromatin and other 

 substances. As will be seen later, it seems possible at least 

 in some conditions of the nucleus to see a mesh-work in the 

 living cell, but in general HARDY'S experiments seem to indi- 

 cate that living protoplasm has none of the structures that 

 have been ascribed to it, and that, apart from the bodies 

 which are almost always included in it, it is structureless. 

 As a matter of fact, the three chief hypotheses of the struc- 

 ture of protoplasm (reticular, alveolar and granular) all de- 

 pend very largely, for their observational basis, on investiga- 

 tions upon protoplasm containing quite definite inclusions. 

 Many observers, for example, have regarded the Echino- 



