104 THE STORY OF LIFE'S MECHANISM. 



thought, in the first place, that it consists of 

 two quite different substances. There is a some- 

 what solid material permeating it, usually re- 

 garded 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 protoplasm 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 reticulum there is 

 found a liquid, perfectly clear and transparent, 

 to whose presence the liquid character of the 

 protoplasm is due (Fig. 23, b). 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 pur- 

 pose, however, whether the fibres are to be re- 

 garded 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). 



