FACTORS AFFECTING STRATIFICATION AND BREAKING I33 



M MgClg, and centrifuged in fresh similar solutions with a measured 

 amount of isosmotic sugar solution at the bottom of each tube to 

 keep the eggs suspended (E. B. Harvey, 1945). It was found that they 

 stratify with decreasing readiness (indicating increasing viscosity) in 

 the following order: CaClg > MgClg > Sea water > NaCl > KCl. 

 They break into "halves" with decreasing readiness in the reverse 

 order, those in CaClg which stratify best break least readily. In the 

 bivalent salts they stratify better and break less readily than in sea 

 water, and in the monovalent salts they stratify less and break more 

 readily than in sea water. The ease of breaking must be determined 

 by an effect of the salts on the surface layers rather than by their effect 

 on the interior viscosity. Heilbrunn (1923, 1928) gives a similar series 

 for viscosity, except that Na and K are reversed. 



No change in size of halves was noted in the different salt solutions, 

 but the percentage of eggs which broke into two when centrifuged at 

 10,000 X g for 4 minutes was as follows: KCl, 99%; NaCl, 90%; sea 

 water, 50%; MgCla, 20%; CaCl2, none. The rate of stratification was 

 the reverse of the above, i.e., the eggs in CaClg were best stratified 

 (E. B. Harvey, 1945 and Plate XV). 



d. Temperature, Pressure, Radiation 



According to Costello (1934, 1938) the amount of stratification de- 

 creases with decrease in temperature, the eggs break less readily, and 

 the red halves are smaller. I have obtained somewhat different results, 

 due probably to difference in procedure. There seems no doubt, how- 

 ever, that eggs kept for three or more hours at 8° C. stratify better 

 and a larger percentage break into two than among those kept at 23°, 

 when centrifuged at the same time. Moreover, eggs are usually con- 

 siderably stratified by gravity on standing overnight at 8° C, but do 

 not stratify at room temperature. 



Under increased hydrostatic pressure unfertilized eggs stratify more 

 rapidly (Brown, 1934) and break into halves more easily (E. B. Harvey 

 and Brown, unpub.). 



After treatment with x-rays or ultraviolet light the eggs break more 

 readily (E. B. Harvey, 1940, 1950, unpub.). According to Cheney 

 (1949 a) they stratify less easily and break less readily in 0.1% caffeine 

 than in sea water. 



e. Fertilization 

 When the eggs are fertilized first and then centrifuged, they stratify 



