622 STUDIES IN GENEKAL PHYSIOLOGY 



unfertilized egg of Arbacia can be caused to develop into a 

 platens. 1 This consists in treating the unfertilized egg for 

 two hours with a mixture of about equal parts of a 2 n 

 MgCl 2 solution and sea-water. It is of theoretical interest 

 to find how this treatment may possibly affect the egg sub- 

 stance. The bulk of our protoplasm consists of proteids, 

 which according to their physical behavior belong to the 

 colloidal substances. The proteids are characterized by two 

 qualities which are of the utmost importance in the analysis 

 of life phenomena. The proteids change their state very 

 easily, and readily take up or lose water. It is more than 

 probable that one or both of these qualities may account 

 for muscular contractility and protoplasmic motion. The 

 agencies which affect these two variable qualities of the 

 protoplasm most powerfully are, first of all, certain enzymes 

 (for instance, plasmase, trypsine, etc.). Almost equally 

 powerful are ions in certain concentrations. As I have 

 dwelt upon this point in my three preceding publications, 2 

 it need not be repeated here. But I wish to call attention 

 to a most interesting paper by Dr. E. Pauli, which has 

 recently appeared and which throws more light on this sub- 

 ject. 3 The third agency is temperature. 



In our experiments it was evidently the second factor 

 which affected the condition of the colloids. The transitory 

 treatment of the unfertilized eggs with a mixture of equal 

 parts of a 2 n MgCl 2 solution and sea- water brings about a 

 change in the physical conditions of certain colloids which 

 is not reversed by putting them back into normal sea-water, 

 and which allows them to develop into normal plutei. 



As far as the spermatozoon is concerned, it may bring 

 about the same change in the condition of the colloids in 



1 1 have not been able to raise the fertilized eggs of Arbacia beyond the pluteus 

 stage in the laboratory. 



2 Part II, pp. 539, 544, and 559. 



3 PAULI, Archivfur die gesammte Physiologie, Vol. LXXVIII (1899), p. 315. 



