Chapter XX 



SUMMARY AND CONCLUSIONS 



In the account which has just been given, an endeavor has 

 been made to set forth all the facts now known concerning the 

 cytoplasm and the considerable progress which has been made dur- 

 ing these last years with regard to this important question. Until 

 1910, there were only hypothetical and quite fragmentary data on 

 the cytoplasm, although the nucleus had been exclusively studied. 

 At the present time, the subject of the physical constitution of the 

 cytoplasm has made rapid progress and its morphological consti- 

 tution is today definitively clarified. In concluding this volume, 

 it is well to summarize the knowledge which we possess on the 

 subject at the present time, in order to bring out essential features 

 and, above all, to give a comprehensive view of the morphological 

 constitution of the cytoplasm. 



Recent investigations have shown the cytoplasm to be a very 

 complex heterogeneous structure. 



Cytoplasm:- It is now proved that the cytoplasm, to which cy- 

 tologists until 1908 had attributed a special structure, generally 

 reticular or alveolar, appears, on the contrary, as a homogeneous 

 and transparent substance. It is essentially composed of a 

 lipoprotein complex (protein, about 55% and lipides about 

 15% of dry weight) in pseudosolution in water (about 80-90%) 

 containing mineral salts. Cytoplasm offers characteristics inter- 

 mediate between liquids and solids. It is fluid, it moves and it 

 exhibits surface tension, i.e., whenever it is extracted from the 

 cell it tends to take the shape of minimum surface, namely, the 

 spherical form. These are properties of liquids. But it also has 

 rigidity, giving it a torsion elasticity which is a property of solids. 

 Its viscosity has been measured and found to vary according to the 

 physiological state of the cell and the physical condition in which 

 the cell is placed. Its viscosity is always superior to that of water 

 but may be very much higher and comparable to that of glycerine 

 or even of oil of vaseline. In dehydrated organs, the cytoplasm 

 may become more or less solid. 



Since the celebrated work of Mayer and Schaeffer on animal 

 cells (1908), confirmed by that of Laficque, Becquerel and GuiL- 

 LIERMOND on plant cells, it has been recognized that the cjrtoplasm 

 of living cells always appears optically empty under the ultramicro- 

 scope, just as do solutions of nucleoprotein. The cytoplasm behaves 

 like an electronegative hydrogel. Like all gels, alkaline or nega- 

 tive, it becomes cloudy when acids are introduced into it: First 

 luminous streaks, then ultramicroscopic granules are seen to 

 appear, and the cytoplasm is transformed into a network of gran- 



