164 FINE-STRUCTURE OF PROTOPLASM II 



ment. The most striking of these effects \& protoplasmic flow, and when 

 seen for the first time this phenomenon will always convince the 

 observer of the liquid state of the cytoplasm. 



The merit of having characterized the aggregate state of cytoplasm 

 with the aid of physical laws is due to Rhumbler (1914)- According 

 to his observations, the cytoplasm of the amoeba possesses i. no 

 measurable elasticity, 2. no perceptible compressibility at ordinary 

 pressures and 3. it follows the capillary laws which are determined by 

 the surface tension (minimum surface, constant contact angle, spread- 

 ing on the surface of liquids, capillary rise). At the present time our 

 picture will be somewhat different. 



According to Newton's law, ideal Hquids are completely free from 

 inner elasticity: any particle in the bulk of 'the liquid can be moved 

 at will without showing the slightest tendency to swing back into its 

 original position. In cytoplasm this condition is not fulfilled, for, as 

 will be shown below, it possesses structural elasticity or elasticity of flow. 



The incompressibility should not be tested at "ordinary" pressures, 

 but at high pressures where the low compressibility in comparison 

 with solid bodies becomes apparent. If a living amoeba in its nutrient 

 is exposed to a uniform pressure of the order of magnitude required 

 to prove incompressibility, its cytoplasm is altered, whereas it is the 

 main property of ideal liquids not to undergo any changes in this 

 experiment. Brown (1934) and Marsland (1942) show that the cyto- 

 plasm of different eggs, of Amoeba, Paramaecium, of human erythro- 

 cytes and of Elodea leaves becomes liquefied by high hydrostatic 

 pressure. It behaves therefore Uke sols in which the process of gelation 

 is accompanied by a small increase of volume. According to obser- 

 vation in the centrifuge microscope with a high pressure chamber, the 

 mobility of included particles increases by almost 25% for each 

 pressure increment of 70 atm. (1000 lbs/in.^). Under these conditions 

 protoplasmic streaming is inhibited, and within fairly broad limits, 

 the effect is reversible. Pressure up to 300 atm. may be maintained 

 for about an hour, and yet, when the cells are returned to atmospheric 

 pressure, the original structural characteristics are restored within a 

 minute. At 700-1000 atm. even the cortical layer of the cytoplasm is 

 liquefied and irreversible changes begin to appear. 



Rhumbler's best arguments refer to the capillary properties of 

 naked cytoplasm, although by no means all cytoplasts assume a 



