DEPARTMENT OF MARINE BIOLOGY. 203 



Changes in the Cortical Layer. 



When eggs became stale a number of changes took place shnultaneously, 

 namely, loss of egg-jelly, increase in the size of the egg, absence of fertiliza- 

 tion membrane, gelatinization of the cortical layer of the egg, etc. These 

 changes are explicable in tenns of a chemical change which causes the outer 

 layers of the egg to be dissolved and which changes the permeability of the 

 cortical layer with a consequent intake of sea-water. The aging process 

 proper corresponds with the period of changed permeability, and it may be 

 experimentally shortened by hypertonic solutions of sea-water. 



An examination of the sea-water at the Tortugas disclosed the fact that 

 when tested by colorimetric methods as well as by the electric potentiometer, 

 which determinations were made by Professor McClendon, the hydrogen 

 concentration of the sea-water was PH 8.1 to 8.2. It is this relatively 

 large excess of free hydroxyl-ions in the sea-water which is responsible for 

 (1) the dissolution of the egg-jelly, (2) the changes in the cortical layer with 

 the consequent intake of water, and (3) the accelerated respiration that 

 takes place in aging eggs; and, if this assumption be correct, it follows that 

 with an increase of the free hydrogen-ion concentration to the neutral point 

 these deleterious changes would be retarded or minimized or possibly pre- 

 vented and the longevity of the egg correspondingly increased; conversely, 

 in hyperalkaline solutions of sea-water the mortality would be accelerated. 



Many experiments were made along these lines. At different intervals 

 the eggs in the following solutions were tested, namely: in sea-water, in sea- 

 water made neutral, sea-water made slightly acid, sea-water made hyper- 

 alkaline. A number of errors in these experiments were later corrected in 

 experiments with Arhacia at Woods Hole, but the general results are clear 

 and in striking accord with expectation. Eggs kept in neutralized sea-water 

 were longer-lived than control eggs and showed less developmental irregu- 

 larities than the controls, and longevity was decreased with hyperalkaline 

 solutions. 



Respiration of Aging Eggs. 



With the aid of a manometer suggested by Professor McClendon, and 

 which gave direct readings of the oxygen consumption, it was possible to 

 obtain continuous readings of the respiration of a sample of eggs from the 

 time of shedding to the death of the unfertilized eggs. Corresponding records 

 were obtained for the fertilized eggs. The data were plotted and showed 

 for the unfertilized eggs a gradual increment in the oxygen consumption for 

 the first 5 to 6 hours, then a plateau for 2 hours, during which time respi- 

 ration is maintained at a uniform rate, and then a sharp rise in the rate of 

 oxidation. The last part of the curve continues till all the eggs are disin- 

 tegrated. The curve so obtained is parallel with the curves for egg-jelly 

 dissolution and the curve for increase in volume with age, and it serves as 

 another and parallel index of the rate and measure of the aging process 

 in eggs. The sharp rise in oxygen consumption occurs when the jelly is 

 dissolved completely from all or nearly all the eggs, when the cortical layer 

 is permeable to sea-water and enlargement has taken place, and when death 

 of the eggs is rapidly taking place. 



These studies have thrown light upon the nature of the changes that take 

 place when eggs become increasingly stale, and they indicate how aging may 

 be prevented, either by retarding the respiratory rate, as Loeb has so beauti- 

 fully demonstrated, or by preventing the dissolution of the cortical layer 

 of the egg, as I have merely outlmed in this summary. 



