PHYSICO-CHEMICAL PROPERTIES. 99 



physiologist J. LOEB, and rediscovered under the most 

 varied conditions by his numerous pupils. We can only 

 touch upon these investigations here. That they har- 

 monize with our own findings and represent only an ex- 

 pression of the general principle common to them all 

 is, however, readily discernible. The starting-point of 

 LOEB'S investigations is the question of the significance 

 of the different ions of sea-water for the life processes of 

 marine animals. A great similarity was found to exist 

 between the effects of various ions upon phenomena of 

 development and upon the activities of muscle and nerve. 

 An interesting example is furnished by the development 

 of the eggs of Fundulus, a small bony fish. These fish 

 are able to develop not only in sea-water but also in dis- 

 tilled water. If immediately after fertilization these eggs 

 are introduced into a sodium chloride solution of the 

 concentration of the sea-water they all die in the course 

 of a few hours without developing any further. If, 

 however, a small amount of calcium, which also represents 

 a constituent of the sea-water, is added to the sodium 

 chloride solution, normal embryos are produced. A 

 pure sodium chloride solution is poisonous also for the 

 adult animals, but this toxicity, too, is done away with 

 upon the addition of a little calcium. Instructive also 

 are the effects of ions on the rhythmical contractions of 

 the swimming-bell of medusae. After removal of the 

 central nervous system in these animals the bell still con- 

 tracts rhythmically in a pure sodium chloride solution. 

 These contractions cease, however, as soon as certain 

 cations, such as calcium and strontium, are added to the 

 solution, just as they cease in sea-water. In a similar 

 way, the poisonous effects of pure sodium chloride on 



