ABSTRACT
Sea-urchin spermatozoa {Echinus esculentus) are extremely sensitive to changes in the pH of the suspending medium, their respiration being proportional to pH between 7· 6 and 8· 4.
In a manometric experiment in which semen was diluted 1·25 with sea water (CO2 absorbed), the pH of the suspension was 7· 5 at the beginning of the experiment and 8· 2 at the end, after 180 min. incubation at 150 C.
Sea water, buffered with glycyl glycine, 0-025 M and brought to pH 8 3, was added to a sperm suspension whose pH was 7· 5 at the beginning of the experiment, after a period of incubation. There was a pronounced respiratory Dilution Effect. When the sea water was buffered with glycyl glycine and brought to pH 7·8, and this diluent was added to the same sperm suspension, there was a negligible respiratory Dilution Effect.
The O2 uptake of suspensions prepared in buffered sea water at pH 8·3 was markedly higher than that in the same buffered sea water at pH 8-o.
These observations cast doubt on the reality of the respiratory Dilution Effect when observed in experiments in which sea water is the suspending medium and respiration is measured by a method involving the absorption of CO2. An exception to this generalization was observed in buffered sea water at a low pH, 7 · 6. In this case, the O2 uptake of dilute suspensions was greater, per unit number of spermatozoa, than that of dense suspensions.
2,4-dinitrophenol, 6 × 10−5 M, stimulated the O2 uptake and depressed the motility of spermatozoa more in dense than in dilute suspensions. Versene, 10−3 M, reversed the action of 2,4-dinitrophenol.
The results of other workers on adding suspensions of usnic acid to sea-urchin spermatozoa were not confirmed. This substance is more toxic to spermatozoa in dilute than in dense suspensions.
Throughout this paper ‘x × 102/ml. ‘means ‘x × 108’ spermatozoa/ml’.
Further experimental details will be found under Material and Methods.
Dr E. B. Harvey told me that the semen of A. punctulata contains about 2 × 1010 spermatozoa/ml.
