18 PHYSIOLOGY 



cellular animals, for the service of the other cells of the organism. 

 Others of these granules may represent reserve material, i.e. excess 

 of nourishment which has been put aside by the cell in an insoluble 

 form, to serve for its subsequent needs in times of scarcity. 



THE PHYSICAL STRUCTURE OF PROTOPLASM.. Owing to the 

 close similarities which exist between the fundamental properties of 

 all living organisms, histologists have sought to discover some corre- 

 sponding uniform morphological organisation of the physical basis of 

 these phenomena, namely, protoplasm. 



It is often impossible, even under the highest powers of the micro- 

 scope, to make out any structure whatsoever in the cytoplasm, which 

 is spoken of then as hyaline. In most cases examination of a cell, 

 even unstained, shows some differentiation between a more or less 

 regular framework or meshwork and a more fluid portion filling up its 

 interstices, and these appearances are still more manifest when the 

 cells have been fixed by various hardening fluids. All the results 

 obtained in this manner must be regarded with some suspicion, since, 

 as has been shown by Fischer and by Hardy, it is possible to imitate 

 artificially the various structures, which have been assigned as 

 characteristic of protoplasm, by hardening a homogeneous colloidal 

 solution such as egg-white by different methods and with different 

 agents. The theories of protoplasmic structure can be classified under 

 three heads : 



1. THE GRANULAR THEORY OF ALTMANN. By the use of certain 

 hardening reagents, a dense mass of spherical or rod-shaped granules 

 may be demonstrated in almost all cells of the body (Fig. 4). These 

 granules have been regarded by Altmann as the elementary particles 

 of life, and he locates in them the various vital functions, the sum of 

 which make up the life of the cell. According to Altmann these granules 

 can only arise from the division of pre-existing granules, and he has 

 formulated the phrase omne granulum e granulo, which is a further 

 extension of Virchow's sentence omnis cellula e cellula. It is probable 

 that a number of different kinds of structures of varying importance 

 are included among Altmann's granules. In some cases they are the 

 products of the activity of the cytoplasm and, as in secreting cells, 

 will be later on cast out with water and salts as the specific secretion. 

 In other cases they may be cell organs or plastids with the special 

 metabolic functions assigned to all granules by Altmann. In many 

 cases no treatment whatever will display the existence of granules. 



2. THE FIBRILLAR THEORY. By the employment of appropriate 

 methods of hardening, it is easy in most cells to demonstrate a network 

 or clusters of fibrils which form, so to speak, a denser part of the cell. 

 This fibrillar network has been named the ' spongioplasm ' in contra- 

 distinction to the structureless material filling its meshes known as 



