Febbcary 8, 1918] 



SCIENCE 



147 



found by Jones and Guy. Solutions of 

 hydrated salts were in general more 

 transparent than pure water, especially 

 at the centers of the absorption bands. 

 Solutions of non-hydrated or only 

 slightly hydrated salts are more 

 opaque than pure water, especially at 

 the centers of the bands." 

 The quantitative conclusions are based on 

 the two assumptions that the van't Hoff for- 

 mula holds absolutely when the true concen- 

 trations are used, and that the percentage dis- 

 sociation can be calculated from the conductiv- 

 ity. Unfortunately, neither of these assump- 

 tions is true. There are many who think very 

 highly of Jones' work and there are those who 

 are more critical. All will agree, however, 

 with the words of Professor Eeid in the bio- 

 gi-aphical sketch, that Jones was an advocate 

 rather than a judge. Wilder D. Bancroft 



SPECIAL ARTICLES 



COMP.\RATIVE PERMEABILITY OF FERTILIZED 

 AND UNFERTILIZED EGGS TO WATER 



In general the rate of the osmotic entrance 

 or exit of water, in any living cell, after 

 transfer from its noiTnal medium to another 

 non-injurious medium (i. e., one not impair- 

 ing semi-permeability) of lower or higher 

 osmotic pressure, varies directly (1) with the 

 gradient of osmotic pressure between the in- 

 terior and the exterior of the cell, (2) with 

 the area of the semi-permeable membrane 

 enclosing the cell, and (3) with the perme- 

 ability of this membrane to water. It is to 

 be exi)ected that this permeability to water 

 will vary in different physiological states of 

 the cell; and that the same species of cell, 

 placed in the same medium, will show varia- 

 tions in the rate of the osmotic transfer of 

 water, i. e., in its rate of swelling or shrink- 

 age, according to its physiological condition 

 or state of functional activity at the time 

 of the transfer. There is in fact a definite 

 and constant difference between the fertilized 

 and the unfertilized eggs of the sea-urchin 

 Arbacia in this respect, fertilization being 

 followed regularly by a marked increase in the 

 pei"meability of the egg-surface to water — as 



may readily be shown by bringing tlie eggs 

 into either dilute or concentrated sea-water; 

 in the former medium they swell, in the latter 

 they shrink, but in both cases the rate of the 

 process is much greater in the fertilized than 

 in the unfertilized eggs. In the unfertilized 

 egg-s both swelling and shrinkage are surpris- 

 ingly slow, so that in a medium whose osmotic 

 pressure differs from the normal by so much 

 as ten or twelve atmospheres these eggs show 

 little apparent alteration of size at a time 

 (e. g., two minutes after placing in this 

 medium) when the fertilized eggs are con- 

 spicuously swollen or shrunken. This differ- 

 ence of behavior relates entirely to the rate 

 at which water either enters or leaves the 

 egg; the degree of swelling or shrinkage when 

 osmotic equilibrium is reached is approxi- 

 mately the same in both cases. It is clear 

 therefore that this difference has nothing to 

 do with any possible change in the osmotic 

 pressure of the egg-protoplasm, resulting from 

 fertilization, but is determined simply by the 

 greater readiness with which water enters or 

 leaves the fertilized as compared with the un- 

 fertilized egg. According to former measure- 

 ments made on the rate of swelling of ferti- 

 lized and unfertilized eggs in dilute sea-water, 

 the resistance to the passage of water across 

 the plasma-membrane is decreased approxi- 

 mately four times as a result of fertilization.' 



The most striking and convenient method 

 of showing this difference is to place a mix- 

 ture of equal numbers of unfertilized and 

 fertilized uncleaved eggs (the latter ferti- 

 lized at least 15 minutes previously) in a 

 somewhat strongly hypertonic sea-water (e. g., 

 1 volume of van't Hoff's artificial sea-water 

 of 2.5 m concentration plvs 4 volumes normal 

 sea-water). The fertilized eggs at once shrink 

 rapidly and undergo crenation, and within 

 less than one minute exhibit a collapsed, 

 shrimken, and angular appearance; at this 

 time the unfertilized eggs show little change, 

 so that a striking contrast is presented. 

 Shrinkage continues slowly in the unferti- 

 lized eggs, and becomes well marked in the 

 course of five or six minutes, but a curious 



1 Amer. Jour. Physiol, 1916, Vol. 40, p. 249. 



