THE STRUCTURE OF PROTOPLASM 



245 



probably built up of finer ultramicroscopic, invisible fibers, 

 present in living tissue generally. 



The Reticular Hypothesis. — Linear structural units may be 

 oriented so as to form an entanglement such as exists in a brush 

 heap, or they may be arranged in a more orderly manner in the 

 fashion of a three-dimensional net. Earlier controversies often 

 centered on the question whether protoplasmic fibers are dis- 

 continuous or anastomose to form a net, or reticulum. The 

 meshes of the supposed protoplasmic net were said to be from 



Fig. 123.— The fibrous kino- 

 plasm (above) and emulsion of 

 trophoplasm (below) in an egg of 

 Marsilia. {After Haberlandt from 

 Strasburger.) 



Fig. 124. — The fibrous structure of 

 sinew from the frog as seen with dark- 

 field. (From G. Ettisch.) 



3^ to 2 /x in size. Whether the purely anatomical framework 

 or the "hyaloplasm" ("enchylema") which bathes it is the real 

 living substance was judged in favor of the latter. 



The concept of a reticulum as the structural framework of 

 protoplasm has persisted in medicine in the widely recognized 

 stroma of the red blood cell. The stroma is presumed by Bech- 

 hold to be a delicate, weblike net, peripherally located. Micro- 

 dissection studies fail to reveal any such framework either in 

 the large (nucleated) amphibian erythrocyte or in the human 

 corpuscle. The concept is a justifiable one and, as a general 

 hypothesis of the ultramicroscopic structure of protoplasm, finds 

 ample indirect evidence in other material, but there is no visible 

 framework of a substantial nature in the living cell; as for the 

 red blood cell, it is simply a sac (see page 60). 



