238 PROTOPLASM 



thing, viz., a droplet; they all become, therefore, emulsions 

 in one form or another. Even the granular hypothesis now 

 belongs under this heading, for Spek has seen the most 

 minute of protoplasmic granules fuse and form larger liquid 

 globules with discernible contours. (Some solid granules, 

 such as crystals, occur in protoplasm.) We thus recognize one 

 main type of visible structure in living protoplasm, viz., an 

 emulsion. The various distinctive names which have been given 

 to this structure indicate, in part, the actual particular con- 

 figuration assumed by the emulsion and, in part, the author's 

 interpretation of it as it exists in the particular material he has 

 investigated. 



The Granular Hypothesis. — The observation of Spek just 

 referred to indicates that protoplasmic "granules" are usually 

 fluid droplets, as it has long been suspected that they might be, 

 for solid material is not compatible with life; but granules they 

 were in the minds of the older investigators. Protoplasmic 

 granules were called microsomes by Hanstein (1882). Biitschli 

 remarked that they thereby obtained the right of entry among 

 the privileged and recognized units of protoplasmic structure, 

 for "anything that is called by a Greek name at once seems to 

 many people to be much better known, and as something which 

 must be definitely reckoned with." What Biitschli says is 

 quite true, but, after all, the granules must be reckoned with for 

 reasons other than their Greek name. Altmann, who is usually 

 regarded as the author of the granular hypothesis of proto- 

 plasmic structure, went so far as to suggest that the granules 

 may be living bacteria. The cell thus became a colony of 

 minute organisms. The idea that certain protoplasmic inclu- 

 sions are bacteria appears again and again in biology. Mito- 

 chondria were once regarded as such and were therefore assumed 

 to have a certain autonomy of their own apart from the cell. 

 The rapid motion of rod-shaped mitochondria in a living tissue- 

 culture cell (fibroblast) certainly suggests that these inclusions 

 get about quite independently. However, that they are bacteria 

 seems unlikely. 



Of the physical and chemical constitution and physiological 

 significance of protoplasmic granules little is known. Undue 

 importance has been attached to many of them, and it is, after 

 all, as Harper says, a motley collection which is brought together 



