3IO L. V. HEILBRUNN. 



protoplasm itself. This can very simply be done by the centri- 

 fuge method. In a recent paper on cell division 1 I have recorded 

 a number of measurements of the viscosity of the anesthetized 

 protoplasm of sea-urchin eggs. The method of measurement is 

 described there as well as in a previous paper. 2 These results 

 give the effect on protoplasmic viscosity of various anesthetics 

 at the very concentration at which they are effective in producing 

 anesthesia. 



One fault that might perhaps be found with some of the pre- 

 vailing theories of anesthesia is that they are based for the most 

 part on very general evidence. It is only rarely that any due 

 process has been thoroughly studied. And yet in order to under- 

 stand anesthesia in general it is perhaps essential first to concen- 

 trate attention on some one process, preferably a simple one. An 

 explanation of this single case can then perhaps be applied to 

 other cases. 



I have studied particularly the process of cell division in sea- 

 urchin eggs. Anesthesia in sea-urchin eggs was first studied by 

 Fiihner 3 who interpreted his results as favoring the Overton- 

 Meyer theory. R. S. Lillie* later determined the effective con- 

 centration for many anesthetics. He also attempted to show that 

 anesthetics decrease the permeability of the plasma-membrane. 5 



In the process of cell division in the sea-urchin egg I have 

 shown that there are certain marked viscosity changes. 6 These 

 are always present. First there is a sharp increase in viscosity 

 and this is followed by a decrease. 



What then is the effect of anesthetics on the cytoplasmic vis- 

 cosity of these eggs ? In seeking to answer this question we must 

 study every substance which prevents cell division without killing 

 the egg. Even those substances which produce injurious effects 

 must be considered. According to some writers these are not 

 true anesthetics, but such a distinction is not a wise one. Prac- 

 tically every anesthetic produces some injury if the exposure is 



1 Heilbrunn, L. V., /. Exp. Zool., 1920, XXX., 211. 



2 Heilbrunn, L. V., BIOL. BULL., 1915, XXIX., 149. 



3 Fiihner, H. ., Arch. Exp. Path. u. Pharmacol., 1904, LIT., 69. 

 4Lillie, R. S., /. Biol. Chem., 1914, XVII., 121. 



5 Lillie, R. S., Amer. J. Physiol., 1918, XLV., 406. 

 Heilbrunn, L. V., /. Exp. Zool., 1920, XXX., 211. 



