118 The Mechanistic Conception of Life 



well known, if we have a salt in solution, e.g., sodium chloride, 

 we have not only NaCl molecules in solution, but a certain 

 number of NaCl molecules are split up into Na ions (Na atoms 

 charged with a certain quantity of positive electricity) and CI 

 ions (CI atoms charged with the same amount of negative 

 electricity) . When an egg is in sea-water, the various ions enter 

 it in proportions determined by their osmotic pressure and the 

 permeability of the protoplasm. It is probable that some of 

 these ions are able to combine with the proteins of the proto- 

 plasm. At any rate, the physical qualities of the proteins of 

 the protoplasm (their state of matter and power of binding 

 water) are determined by the relative proportions of the 

 various ions present in the protoplasm or in combination with 

 the proteins.^ By changing the relative proportions of these 

 ions we change the physiological properties of the protoplasm, 

 and thus are able to impart properties to a tissue which it does 

 not possess ordinarily. I have found, for instance, that by 

 changing the amount of sodium and calcium ions contained 

 in the muscles of the skeleton we can make them contract 

 rhythmically like the heart. It is only necessary to increase 

 the number of sodium ions in the muscle or to reduce the num- 

 ber of calcium ions or do both simultaneously.^ On the basis 

 of this and similar observations I thought that by changing the 

 constitution of the sea-water it might be possible to cause the 

 eggs not only to show a beginning of development but to 

 develop into living larvae, which were in every way similar 

 to those produced by the fertilized egg. 



There seemed to be three ways in which this might be 

 accomplished. The first way was a simple change in the con- 

 stitution of the sea-water without increasing its osmotic pres- 

 sure. The second way was to increase the osmotic pressure 



1 Loeb, J., "On lon-Proteid Compounds and Their Role in the Mechanics of 

 Life-Phenomena," Amer. Journ. of Phys., Ill, 1900. 



2 It is due to the Ca ions of our blood that the muscles of our skeleton do not 

 beat rhythmically, like our heart 



