96 



GENERAL PHYSIOLOGY 



motion, in the second they are moving somewhat more slowly, and 

 in the last still more slowly. Since, therefore, only a gradual 

 difference exists, it is impossible to establish a sharp limit. In 

 living substance also there are different grades of mobility among 

 the particles,, i.e., in one case the substance is like thin, in another 

 case like thick liquid. In general, it possesses the consistency and 

 mobility of raw white of egg, but it may be firmer, and certain 

 constant differentiations of protoplasm may possess even the con- 

 sistency of a soft jelly approximating a solid condition, without 

 losing, however, the power of shifting its particles. Such a condi- 

 tion exists in muscle-fibres, flagella, cilia, the nucleus, and upon 

 the surface of many protoplasmic masses that do not possess a. 



FIG. 36. Orbitolites. Piece of the many-chambered calcareous disc, bearing outstretched pseudo- 

 podial filaments. A , Undisturbed. B, By strong shaking the protoplasm of the pseudopodia 

 has been stimulated to form globules and spindles. 



membrane, such as infusorian cells. The term . solid is applicable 

 to such cases only, if at all. But these cases of a more viscous con- 

 sistency are always locally restricted within the cell ; the rest of 

 thfe cell-contents is always a thinner liquid. 



Finally, it should not be forgotten that within the liquid there 

 may be deposited all sorts of solid elements of very various con- 

 sistencies, and that, therefore, the whole constitutes, not a homo- 

 fBneous liquid, but a mixture, or, as Berthold terms it, an emulsion, 

 or this reason it appears inadmissible to speak of an " aggregate 

 condition " of protoplasm, as many observers do. Strictly speaking, 

 the term " aggregate condition " can apply only to a homogeneous 

 substance, not to a mixture containing substances that possess in 

 themselves very various aggregate conditions. 



