Guilliermond - Atkinson — 12 — Cytoplasm 



of glycerin and then that of bread dough and may even attain and 

 exceed that of vaseline. 



In the egg of Fucus the cytoplasm becomes more and more 

 viscous as the egg matures and its exchanges diminish. Immedi- 

 ately after fertilization it again becomes liquid and remains in 

 this state in the embryo. Areas seem to exist in the egg, there- 

 fore, where fluidity is more accentuated, — sort of centers of activity 

 where different chemical exchanges are produced. 



It appears from all these observations then, that the viscosity 

 of cytoplasm is always superior to that of water and in numerous 

 cases as great as that of blood. Yet in certain cells, especially in 

 old organs, the viscosity can be much higher. Moreover in dehy- 

 drated organs, seeds, for instance, the cytoplasm can be more or 

 less solid. 



Many attempts have been made to measure directly the viscosity 

 of the cytoplasm inside the cells. The easiest method to employ is 



that which makes use of the law for 

 falling spheres established by the 

 physicist Stokes. The cytoplasm of 

 certain cells encloses starch grains 

 which are more dense than the cyto- 

 plasm and which have a tendency, 

 because of their weight, to fall 

 through the cytoplasm to the lowest 

 point in the cell. By using an hori- 

 FiG. 7. — Ruptured siphon of zontal microscope, the time required 



Vaucheria showing tendency of lobed n ,■, • j^j?ii'ii • i 



extruded contents to break up into for the grams to fall IS detcrmmcd 



globular drops. At left, one droplet ^nd, by applying the physicist's form- 

 greatly magnified. (After VAN Tie- , ' ,, ^. "^ ., « j, . i 



GHEM and cosTANTiN). ulac, thc viscosity oi the cytoplasm is 



calculated. 



By this process of determining the speed with which starch 

 grains and certain crystals fall through the cytoplasm, Weber was 

 able to state that the viscosity of the cytoplasm varies with the 

 cell under consideration. It seems to increase with the age of 

 the cells. Certain influences (increase in temperature, the action 

 of certain chemical substances, such as narcotics) can also cause 

 variations. 



Heilbronn has employed the following method : an iron needle, 

 very fine but too heavy to be carried about in the cytoplasmic cur- 

 rents, is introduced into a Plasmodium. The needle being located 

 under the microscope, an electro-magnet in which flows a current 

 of increasing intensity, is brought near the preparation. When the 

 needle in the field of the microscope begins to orient itself in the 

 direction of the lines of force, the experiment is stopped. The 

 intensity of the current necessary to produce a visible deviation of 

 the needle is divided by the intensity producing the same effect on 

 the same needle plunged into pure water. With the viscosity of 

 water thus taken as a standard, the quotient measures the viscosity 

 of plasmodial protoplasm. 



