July 22, 1910] 



SCIENCE 



123 



presence of oxidases within the egg or to an 

 increase in the permeability of the egg to 

 oxygen or carbon dioxide. The carbon diox- 

 ide might diffuse as ions or undissociated 

 molecules, the oxygen only in the latter form. 

 The lipoids of which the protoplasm is largely 

 composed are relatively impermeable to ions. 



With a view toward a decision between the 

 above-mentioned views I studied the perme- 

 ability of the egg of Lytechinus (Toxop- 

 neustes) variegatus to ions, at the Carnegie 

 Laboratory at Tortugas, Ma. Since the ions 

 alone carry the electric current through a 

 solution, it was thought sufBcient to measure 

 the electric conductivity of the eggs (by the 

 method of Kohlrausch). 



The conductivity of the eggs was found to 

 be very much lower than that of the sea water, 

 and to be increased on fertilization or begin- 

 ning of parthenogenesis. For example, in one 

 experiment, the resistance (the reciprocal of 

 the conductivity) of the sea water was 53 

 ohms, that of the unfertilized eggs 595 ohms 

 and that of the same eggs after fertilization 

 455 ohms. In another experiment the resist- 

 ance of the unfertilized eggs was 519 ohms 

 and that of the same eggs made partheno- 

 genetic with acetic acid 485 ohms. 



During each set of experiments, the tem- 

 perature (which was not far from that of the 

 sea) did not vary one tenth of one degree. 

 The amount of sea water mixed with the eggs 

 was kept constant by removing all of the jelly- 

 like coverings, centrifuging the eggs in the 

 conductivity vessel, marking their upper level 

 with a fine pen and indelible ink and centri- 

 fuging them down to the same level before 

 every reading. The conductivity of the sperm 

 and of the acetic acid solution was slightly 

 less than sea water and each was thoroughly 

 washed out with sea water. If the eggs, after 

 having pushed out " fertilization " membranes, 

 were centrifuged down to the former level, 

 some of them were distorted, but this possible 

 source of error was controlled by using eggs 

 that had been washed so long in sea water 

 that membranes were not pushed out in nor- 

 mal nor in parthenogenetic development. The 

 current passed through the eggs was not suffi- 

 cient to stimulate nerve. 



The increased production of carbon diox- 

 ide was not sufficient to account for the in- 

 creased conductivity, for the conductivity of 

 the sea water was not measurably increased 

 by saturating it with carbon dioxide. 



The conductivity of the egg is much lower 

 than that of an aqueous solution of its ash 

 made up to the same volume. This may be 

 due to the resistance of the surface layer, but 

 is partly due to internal conditions as shown 

 by placing the electrodes within the egg 

 (hen's egg yolk). Experiments which I made 

 at Cornell Medical College indicate that this 

 low internal conductivity of the egg is due to 

 the presence of poorly dissociated ion-pro- 

 teid compounds (or adsorpates). The "yel- 

 low " yolk of the hen's egg consists of two 

 non-miscible fluids and fine granules. The 

 two fluids are both solutions containing lipoid- 

 protein compounds and are not of sufficient 

 difference in specific gravity to allow separa- 

 tion by the centrifuge. The granules are 

 probably lecith-albumins and are precipitated 

 by the centrifuge. 



Hen's egg yolk was centrifuged and the top 

 layer, containing very few granules, sepa- 

 rated from the bottom layer, containing nu- 

 merous granules. The following figures rep- 

 resent the elective conductivity (when divided 

 by 100,000) : 



The conductivity of the upper layer de- 

 creases with dilution, but a dilution of the 

 lower layer with one volume of water does not 

 decrease its conductivity. If this failure of 

 dilution to decrease the conductivity were 

 wholly due to the increase in the spaces be- 

 tween the granules (the fluid conducting and 

 the granules insulating) the conductivity of 

 the upper layer diluted with one volume of 

 water would be greater than that of the lower 

 layer at the same dilution, but the reverse 

 being the case shows that the dilution must 

 have caused the liberation of electrolytes 

 from the granules. 



