THE CELL AND PROTOPLASM. 87 



two quite different substances. There is a some- 

 what solid material permeating it, usually, regarded 

 as having a reticulate structure. It is variously 

 described, sometimes as a reticulate network, 

 sometimes as a mass of threads or fibres, and 

 sometimes as a mass of foam (Fig. 23, a). It is 

 extremely delicate and only visible under special 

 conditions and with the best of microscopes. Only 

 under peculiar conditions can it be seen in proto- 

 plasm while alive. There is no question, however, 

 that all protoplasm is permeated when alive by a 

 minute delicate mass of material, which may take 

 the form of threads or fibres or may assume other 

 forms. Within the meshes of this thread or retic- 

 ulum there is found a liquid, perfectly clear and 

 transparent, to whose presence the liquid charac- 

 ter of the protoplasm is due (Fig. 23,^). In this 

 liquid no structure can be determined, and, so far 

 as we know, it is homogeneous. Still further study 

 discloses other complexities. It appears that the 

 fibrous material is always marked by the presence 

 of excessively minute bodies, which have been 

 called by various names, but which we will speak 

 of as microsomes. Sometimes, indeed, the fibres 

 themselves appear almost like strings of beads, 

 so that they have been described as made up 

 of rows of minute elements. It is immaterial 

 for our purpose, however, whether the fibres 

 are to be regarded as made up of microsomes 

 or not. This much is sure, that these microsomes 

 granules of excessive minuteness occur in 

 protoplasm and are closely connected with the 

 fibres (Fig. 23, a). 



The Nucleus. (a) Presence of a Nucleus. If 

 protoplasm has thus become a new substance in 

 our minds as the result of the discoveries of the last 



