Experiments on Permeability of Cells. 129 



attention called to it, but it is difficult to find a paper without a reference to 

 the journal in which it is published. 



The degree of permeability is of importance in development. R. Lillie 

 maintains that too great an increase in permeability causes cytolysis of the 

 egg. Gray^ attempts to explain the abnormality of Echinoderm hybrids 

 by assuming that the foreign sperm produces the wrong degree of perme- 

 ability and this leads to some of the chromatin becoming pathological and 

 being thrown out of the spindle. 



The changes in permeability are probably due to changes in the aggre- 

 gation state of colloids: either proteids, lipoids, or proteid-lipoid combina- 

 tions or associations. Many investigators have looked for such changes 

 with the microscope. That some change takes place at the surface of the 

 egg on fertilization has long been known, but opinions differ as to its exact 

 nature. Spherical concentric surfaces, when viewed tangentially with the 

 microscope, cause optical illusions, and the real structure can not be exactly 

 determined without knowledge of the refractive indices of the substances 

 composing it. Kite, however, claims that a thin layer may be observed on 

 the surface of the unfertilized egg and, on fertilization, this layer absorbs 

 water and swells. He claims to have stained it differentially.^ I do not 

 understand, however, his observations on unstained eggs. He says that 

 this layer which he calls the vitelline membrane becomes more distinct 

 (of different refractive index) from the sea-water on swelling, whereas it is 

 well known that all hydrophile colloids, on swelling, become less distinct 

 and more nearly of the same refractive index as the medium. 



The swelling of this layer might cause an increase in permeability, since 

 the swelling of all hydrophile colloids increases their permeability to water- 

 soluble substances. Lillie, however, believes that a reversible increase in 

 permeability takes place in the superficial layer of the cytoplasm (plasma 

 membrane) and J. Gray who has confirmed my determination of the in- 

 crease in permeability of the egg finds that impermeability returns in 15 

 minutes, whereas Kite's vitelline membrane remains swollen. I consider 

 Kite's vitelline membrane a new name for a colloid postulated by Loeb. 



Mitchell and the author' studied experimentally the role of hydroxyl 

 ions in the increase in oxidation of sea-urchin's eggs, which follows fertili- 

 zation or artificial stimulation. We concluded that the increased perme- 

 ability allows the hydroxyl ions of the sea-water to penetrate the egg. This 

 increase in hydroxyl ions within the egg might increase oxidation. 



CONCLUSIONS. 



The permeability of the egg to ions and perhaps some other substances 

 increases on fertilization. The unfertilized egg is perhaps in a dormant 

 condition and the increase in permeability probably allows a rapid inter- 

 change with the surrounding medium necessary for activity (development). 



' Gray, J. Proceedings of the Cambridge Philosophical Society, vol. 17, p. i, 1913. 

 » Kite. Science, n. 9., vol. 36, p. 562. 191 2. 

 » Jour. Biol. Chem., vol. 10, p. 439. 



