174 



FINE-STRUCTURE OF PROTOPLASM II 



pre-existing mitochondria, similar to plastids, chromosomes and virus 

 particles. Lehmann (1947) has proposed the term hiosomes for such 

 bodies which are characterized by self-multiplication and endowed 

 with specific functional tasks. 



Reticulate ground-cytoplasm. The matrix in which the microsomes and 

 mitochondria are suspended has quite a different aspect, depending 

 on the object under investigation and on the method of fixation used. 



Claude and Fullam (1946) speak of a fibrous ground texture in 

 the cells of the guinea pig liver, Faure-Fremiet and co-workers (1948) 

 of a reticulate ground-plasm in the amoebocytes of the snail. The 

 cytoplasm of the thrombocytes in the blood is hyaline, alveolar or 

 fibrous depending on the fixation with osmic acid, formalin or alcohol 

 (Bessis and Bricka, 1948). Bretschneider (1950a) describes a three- 

 dimensional network 400 A wide, partly beaded strands in the cyto- 

 plasm of ciliates fixed with OSO4. 



It looks as though we are about to have a repetition of the cyto- 

 logical discussions on the structures of fixed cytoplasm as seen in the 

 ordinary microscope, this time with reference to the submicroscopic 

 aspect. It is obvious that only the finest textures observed come any- 

 where near the natural situation, while the coarser textures are only 

 worth while considering in relation to a possible linear coagulation 

 of previously filamentous submicroscopic structural elements. Rozsa 

 and Wyckoff (1950/5 1) have found that the cytoplasm of the dividing 

 cells in the onion root tip yields a beautiful dense reticulate structure 

 with very fine meshes (smaller than 0.05 [x diameter) when fixed in 

 neutral formaHn, whilst every acid fixative (especially OSO4 and acetic 

 acid) furnishes a very coarse cytoplasmic reticulum with almost micro- 

 scopic meshes (0.5 fi diameter). Bretschneider (1950c) has made a 

 systematic study of the influence of fixation on the submicroscopic 

 structure of cytoplasm as seen in the electron microscope, and has 

 tested all the treatments used in cytology on the same subject (root 

 tip of onion). The best fixation is obtained in Champy's and in Kopsch- 

 Regaud's fluids (Fig. 108/1,2), which contain formalin and OSO4 

 combined with chromic acid and potassium bichromate. The hyalo- 

 plasm shows a fine network of thin protein filaments with a diameter 

 of about 160 A forming a regular hexagonal pattern. Pure solutions 

 of formaHn (Fig. 108/4, 5), Bouin's fluid (Fig. 108/5) ^^^ Helly's fluid 

 (Fig. 108/6) yield a slightly coarser network. Substances which 



