VISCOSITY 217 



respect, the microdissection method has some advantages, 

 as it permits the determination of the viscosity of the most 

 minute regions in a protoplasmic mass as well as of larger parts, 

 or "organs," of the cell, the nucleus, the chromosomes, and the 

 protoplasmic membrane. 



The question of change in viscosity due to injury is again 

 applicable, as it is in every method involving the application of 

 instruments or the adding of reagents to protoplasm; but the 

 micrurgist, with his material constantly under observation, soon 

 learns to recognize the first sign of abnormality, such as a sudden 

 change in viscosity, in color, or in granulation. Protoplasm 

 sometimes disintegrates instantly at the slightest touch, but it 

 also often tolerates a great deal of handling without evident ill 

 effect and usually gives quick notice when there is change to 

 the abnormal. 



VALUES 



Anyone reviewing the work done on the viscosity of protoplasm 

 might become discouraged at the results, so great is the range 

 in values, but this is just as it should be. Protoplasm may be 

 of any viscosity above a minimum of ten to twenty times that 

 of water, to the practically infinite value of a firm jelly. 



Values between 800 (that of glycerin) and 8,000 (that of a 

 thick sugar syrup) represent the more usual ones for fluid proto- 

 plasm, though a lower value of 10 or 20 may occur. Bread 

 dough well illustrates the higher viscous state of protoplasm. 

 The maximum values of protoplasmic consistency are reached 

 when gelation (or coagulation) and subsequent dehydration 

 take place. This is true of all protoplasm that is to undergo 

 rest for a long time, as in dormant seeds. An extreme upper 

 value is that of the resting plasmodium of a myxomycete (slime 

 mold). During the winter, the plasmodium of a myxomycete 

 becomes as hard and as brittle as a thin sheet of dry gelatin. It 

 is difficult to realize that this so-called sclerotium of a myxomycete 

 is a piece of living protoplasm, yet bits of it quickly start active 

 growth when put in a moist and warm environment with food, 

 even after being kept in the laboratory for some ten years. 

 The viscosity of such a brittle sheet of protoplasm is infinite. 

 While the dormant protoplasm of a slime mold represents an 

 extreme case of protoplasmic consistency, yet an active plasmo- 



