622 STUDIES IN GENERAL PHYSIOLOGY 
unfertilized egg of Arbacia can be caused to develop into a 
pluteus.' This consists in treating the unfertilized egg for 
two hours with a mixture of about equal parts of a 22n 
MgCl, 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,’ 
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... 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 %n MgCl, 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 
1T have not been able to raise the fertilized eggs of Arbacia beyond the pluteus 
stage in the laboratory. 
2Part IT, pp. 539, 544, and 559. 
3 PAULI, Archiv fiir die gesammte Physiologie, Vol. LXXVIII (1899), p. 315. 
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