1 62 PHYSICAL CHEMISTRY 



(especially fatty acids), alkalis or neutral salts, hypertonic solu- 

 tions, mechanical shocks, thermal changes, electric currents, 

 KCN, lack of oxygen, or anesthetics (McClendon, 1909 b). To 

 these may be added in order to complete the list of parthenogenic 

 agents, soap, bile salts, alkaloids, glucosides, blood sera, ultra- 

 violet rays, and simply pricking with a needle. We thus have 

 a list about as large as the list of stimuli for nerves. In what 

 way all these agents increase the permeability is not known. The 

 discussion of this question should be under the general topic of 

 stimulation. 



The question as to whether the fertilization membrane is pres- 

 ent before fertilization has been much discussed 1 . Harvey 

 (1910 a) says that it is not present, whereas Kite takes the op- 

 posite view. It has been supposed to be formed by the contact 

 of the transparent gel covering the egg with a secretion poured 

 out by the egg at fertilization, since it is absent from eggs that 

 have been washed a long time, during which the gel is removed 

 (McClendon,' 191 1 a). Harvey supposes this washing injures 

 the egg. The * evidences for a secretion are numerous. The 

 frog's egg, and according to Glaser (1914 b) the Echinoderm 

 egg, gets smaller during this secretion. By the formation of this 

 membrane it is merely supposed that a denser or more viscous 

 layer is formed out of. material already present. It has been 

 shown by microdissection that the surface of the unfertilized 

 egg is not as viscous as the fertilization membrane (McClendon, 

 1914 e). Heilbrunn (1915 a) supposes that the viscosity of the 

 whole egg is increased by fertilization, but his proof that this 

 increase in viscosity is not confined to the fertilization membrane 

 is not dear. Loeb supposed the elevation of the membrane to 

 be caused by the secretion of an osmotically active substance of 

 high molecular weight behind it. Kite says the membrane swells 

 and that we see the outer surface of it. It is probably pushed 

 out by the passage inward of water attracted by a colloid, but 

 whether this is due to the osmotic pressure or swelling pressure 

 of the colloid seems less important, as it is not certain that these 

 two phenomena are different. 



Many attempts to cause the eggs to segment with sperm ex- 

 tracts have 'been tried, but positive results have been attributed 

 to impurities or lack of isotonicity (M. Morse, 1912 a). Since 



