IV. VISCOSITY MEASUREMENTS 127 



When an amoeba is exposed to stimulating agents, such as an 

 electric shock, ultraviolet radiation, or mechanical agitation, the vis- 

 cosity of the cortex drops sharply, due apparently to a release of 

 calcium. The released calcium apparently enters into the interior 

 of the cell. There it causes first a drop in protoplasmic viscosity, 

 followed by a sharp increase in viscosity. 



Such a sharp viscosity increase seems to occur in all cells when they 

 are exposed to stimulating agents. Even nerve protoplasm appears 

 to become much more viscous when stimulated electrically {cj. SI). 

 The effect is thought to be due to a clotting reaction similar to blood 

 clotting, and dependent primarily on the entrance of free calcium 

 ion into the cell interior. It is thought that, when a muscle is stimu- 

 lated to contract, when a nerve is excited, and when an egg cell 

 is induced to divide, in all cases a gelation or protoplasmic clotting 

 occurs and that this clotting is similar in its fundamental aspects to 

 blood clotting. 



Fat solvent anesthetics tend to prevent the clotting reaction of 

 protoplasm. Apparently, their action is to prevent binding of cal- 

 cium either in the cortex or the interior of the cell. They cause a 

 liquefaction of the cortex and they tend to prevent gelation of the 

 interior. 



In addition to the fat solvent anesthetics, various drugs and other 

 agents have a marked effect on protoplasmic viscosity. At the pres- 

 ent time, we know something as to the effect of hypotonic and hy- 

 pertonic solutions, acids and alkalies, metallic poisons, heat, cold, 

 radiation, pressure, etc. On the basis of the information already ob- 

 tained, it is possible to draw various conclusions as to the behavior 

 of the protoplasmic colloid. Indeed our knowledge of the colloid 

 chemistry of protoplasm is very largely based on quantitative studies 

 of protoplasmic viscosity. 



F. POSSIBILITIES FOR THE FUTURE 



The most interesting viscosity change in blood is undoubtedly 

 the change that occurs when blood clots. This change is not studied 

 by the ordinary methods of viscometry, but is followed by observing 

 the length of time it takes for shed blood to transform from a fluid 

 sol to a gel with some of the properties of a solid. Clotting times of 

 blood can easily be measured in large tubes, drops, or capillary tubes. 



Unfortunately, the student of blood has devised no quantitative 

 methods for the study of blood clotting within the intact circulation. 



