October 29, 1915] 



SCIENCE 



615 



remains of fruits and seeds, whicii is supposed 

 to be more certainly determinable than leaf 

 impressions. It bas been laboriously compared 

 with recent material in the Kew herbarium and 

 from other sources and is illustrated by en- 

 larged photographs often showing the recent 

 seed by the side of the fossil. One is impressed 

 with the care with which the work has been 

 done and the authors certainly merit the grati- 

 tude of their confreres. I venture to hope 

 that they will feel called upon to give us the 

 benefit of their experience in instituting a com- 

 parison, confessedly difficult, between their 

 Pliocene fruit and seed floras of Eeuver, Teg- 

 «len, Cromer, etc., and the abundant Pliocene 

 floras represented by leaves in France, Italy 

 and throughout southeastern Europe. 



Edward W. Berry 

 Johns Hopkins University, 

 Baltimoee, Md. 



SPECIAL ARTICLES 



THE MEASUREMENT OF OXIDATION IN THE 

 SEA-URCHIN EGG 



Because of its accuracy and convenience, 

 Winkler's method of determining the amount 

 of oxygen in solution has been almost exclu- 

 sively used in the various studies of oxygen 

 eonsumption of sea-urchin eggs. This method, 

 as described in various texts of quantitative 

 analysis, depends upon a chain of reactions, 

 which result finally in the liberation of two 

 atoms of iodine for each atom of oxygen orig- 

 inally present in solution. The investigator of 

 egg oxidations measures the oxygen content of 

 some sea-water before and after eggs have 

 been contained in it. The usual procedure ap- 

 pears to be about as follows : The eggs are en- 

 closed in a 300 c.c. bottle filled with sea-water 

 and tightly sealed. At the conclusion of a cer- 

 tain time interval (usually an hour), the 

 supernatant sea-water is siphoned off into a 

 250 c.c. bottle and tested for oxygen. From 

 the value thus obtained, the oxygen concentra- 

 tion in the 300 c.c. bottle at the conclusion of 

 the experiment can be computed, and thus if 

 the original oxygen content of the sea-water is 

 known, the amount of oxygen consumption is 

 readily obtained by subtraction. 



It is obvious that the ordinary Winkler 

 method of determining oxygen loses its effi- 

 ciency in the presence of any substance which 

 takes up iodine. Now it is a fact that iodine 

 absorbing substances are actually present in 

 sea-water which has stood over sea-urchin eggs. 

 This can best be shown by actual measurement 

 of the iodine absorption of such " egg sea- 

 water."^ These measurements have been made 

 a number of times. They show a small but 

 quite constant value. 



Of course after the eggs have been treated 

 with any cytolytic agent, they give off to the 

 sea-water very much larger quantities of iodine- 

 absorbing substances. 



Analytical chemists have suggested at least 

 two methods of making Winkler determina- 

 tions in the presence of organic substances. 

 Perhaps the Rideal and Stewart method is the 

 one most often used.^ In this method the 

 organic substances are oxidized by potassium 

 permanganate in the presence of sulphuric 

 acid. This method may do very well for most 

 organic substances, but in order to oxidize 

 proteins completely, hot concentrated perman- 

 ganate solutions are necessary, and the dilute 

 solutions recommended by Eideal and Stewart 

 can accomplish but very little in the way of 

 oxidations. The extensive literature on the 

 oxidation of proteins by permanganate solu- 

 tions can not be referred to here; the reader 

 will find many references in Oppenheimer's 

 " Handbueh der Biochemie."^ In actual prac- 

 tise the Eideal and Stewart method has not 

 proved satisfactory. 



Another method is to determine the iodine- 

 absorbing powers of the water which contains 

 organic matter.* In this way a correction is 

 obtained which is added to the value determined 

 by the ordinary Winkler method. In meas- 

 uring egg oxidations, this method is open to 

 the objection that the sample chosen for the 

 correction may not be truly representative of 



1 1, e., sea-water which has stood over eggs. 



2 Eideal and Stewart, Analyst, XXVI., 141, 1901. 



3 Vol. 1, pp. 489^95. 



* Cf. Lunge, ' ' Technical Methods of Chemical 

 Analysis," New York, 1908, Vol. 1, Part II., p. 

 783. 



