2 The Structure of Protoplasm 



matter is very probably due to a specific arrangement of parts, that 

 is to say, to structure. 



Often I am asked by physicists and chemists if much can be hoped 

 for in the way of an understanding of protoplasmic structure. Direct 

 observation, even with the highest powers of the microscope, is too 

 superficial to reveal anything fundamental. Chemical analysis is not 

 productive of significant results because once protoplasm is subjected 

 to severe treatment it is no longer living matter. The very structural 

 features which distinguish it from the nonliving are then destroyed. 



The biologist interprets the basic structure of protoplasm some- 

 what in the same way that a chemist interprets the structure of a 

 compound, namely, by its behavior. The chemist sees nothing of the 

 links, rings, side chains, amino and carboxyl groups which he 

 attaches here and there, yet he builds up a structure with consider- 

 able confidence, which is the justification of stereochemistry. Just so 

 does the biologist work; he interprets the structure of living matter 

 in the light of its known physical properties. But this was not the 

 method of the older biologists, and herein lay their error. They told 

 only of what they saw. 



Protoplasm viewed through the microscope appears to be a 

 suspension of fine granules. On this fact was based the granular 

 hypothesis of protoplasmic structure. Its weakness lay in the diver- 

 sity of the granules and the undue significance given them. Some 

 are admittedly important, as are the plastids and the mitochondria; 

 others, such as fat droplets, are but reserve food. These last are really 

 not granules at all but liquid droplets which make of cytoplasm a 

 fine emulsion. The importance attributed to the "granules" — they 

 were regarded by some as living units, morphologically and physiolo- 

 gically independent of the cell — and the necessary coarseness of any 

 optically visible structure, led to the discarding of the granular 

 hypothesis. 



The belief that the basic structural unit of protoplasm is a spheri- 

 cal body has long persisted and has given rise to numerous hypotheses 

 expressed in terms of granules, globules, alveoli, and micellae. Such 

 suggestions are in part supported by fact. Thus, protoplasm is 

 unquestionably an emulsion, and when the emulsion globules are 

 under pressure and symmetrically arranged they assume the shape 

 of dodeca- or tetrakaidecahedra which are hexagonal in cross section. 

 These latter are alveoli. - 



' Protoplasma 9:177, 1930. 



