The Physiology of Sea-Urchin Spermatozoa

1948 ◽  
Vol 25 (4) ◽  
pp. 353-368
Author(s):  
LORD ROTHSCHILD
Keyword(s):  
Sea Urchin ◽  
Sea Water ◽  
Protective Action ◽  
Wave Length ◽  
Dilution Effect ◽  
O2 Consumption ◽  
O2 Uptake ◽  
Sperm Suspension ◽  
Dense Suspensions ◽  
Dilute Suspensions

1. An investigation has been made into the causes of the interrelated phenomena of Senescence and the Dilution Effect in the spermatozoa of Echinus esculentus. The Dilution Effect is the increase in O2 uptake and in movement observed when a concentrated sperm suspension, obtained by partial dilution of semen, is diluted with sea water. 2. The supernatant sea water obtained by centrifuging partially metabolized sperm suspensions contains no substances which depress the respiration or motility of the spermatozoa of the same species. This supernatant sea water has a small but definite protective action on spermatozoa in maintaining but not increasing their O2 consumption. The effect is enhanced by agitating the suspensions before centrifugation. 3. E. esculentus spermatozoa do not glycolyse aerobically, anaerobically, or in the presence of 5% O2 in CO. The absence of aerobic acid production proves that the reduced O2 uptake per sperm of dense suspensions is not due to a lowering of the pH of the medium. 4. As the Dilution Effect is observed in manometric experiments in which CO2 is continuously and adequately removed, neither accumulation of CO2 nor a reduction in pH resulting from the accumulation of CO2 are responsible for the reduced O2 uptake of dense suspensions. 5. The O2 uptake of dense sperm suspensions (> 109 sperm/ml.) is altered by changes in O2 tension. O2 consumption in 100% oxygen is nearly double that in 10% O2 in N2. An increase in O2 tension has no stimulating action on dilute suspensions. 6. An atmosphere of 100% O2 has a gradual toxic effect on dense and dilute sperm suspensions. 7. Carbon monoxide has a greater inhibitory action on dilute than on concentrated sperm suspensions. 8. The difference between the effects of varying O2 tensions or CO on dense and dilute suspensions is partly, or perhaps wholly, due to gaseous diffusion being a limiting factor. This may partly explain the Dilution Effect. 9. Apart from photo-reversibly inhibiting respiration, CO exerts an irreversible toxic influence on sea-urchin spermatozoa. 10. Illumination of spermatozoa with a wave-length of light outside the region of photo-chemical absorption by CO cytochrome oxidase enables visual examination to be made in the presence of CO. The O2 uptake of a suitable concentration of spermatozoa is 70% inhibited by 5% O2 in CO. The same inhibition occurs when the suspension is illuminated by light of wave-length 548 mµ, but there is no equivalent decrease in motility. 11. After motility and respiration have ceased sea-urchin spermatozoa still contain oxidizable substrates and the appropriate dehydrogenases as evidenced by their ability to reduce methylene blue in an evacuated Thunberg tube.

scholarly journals The Physiology of Sea-Urchin Spermatozoa

1956 ◽  
Vol 33 (1) ◽  
pp. 155-173
Author(s):  
LORD ROTHSCHILD
Keyword(s):  
Sea Urchin ◽  
Sea Water ◽  
Usnic Acid ◽  
Dilution Effect ◽  
O2 Uptake ◽  
Sperm Suspension ◽  
Dense Suspensions ◽  
Cast Doubt ◽  
Dilute Suspensions ◽  
Glycyl Glycine

1. 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. 2. 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 15° C. 3. 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. 4. 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 8.0. 5. 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. 6. 2,4-dinitrophenol, 6 x 10-5M, stimulated the O2 uptake and depressed the motility of spermatozoa more in dense than in dilute suspensions. Versene, 10-3M, reversed the action of 2,4-dinitrophenol. 7. 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.

The Physiology of Sea-Urchin Spermatozoa

1950 ◽  
Vol 27 (1) ◽  
pp. 59-72
Author(s):  
LORD ROTHSCHILD ◽  
P. H. TUFT
Keyword(s):  
Sea Urchin ◽  
Sea Water ◽  
Dilution Effect ◽  
O2 Uptake ◽  
Time Curve ◽  
Sperm Density ◽  
Negative Results ◽  
Catalytic Function ◽  
Sperm Suspension ◽  
Dense Suspensions

1. When a suspension of sea-urchin semen in sea water is diluted, the total O2 consumed and the rate of O2 uptake per spermatozoon are greater than before dilution. This is the Dilution Effect, first described by Gray (1928 a). A further investigation of this phenomenon has been made, using the semen of Echinus esculentus. 2. The form of the O2 uptake-time curve of such suspensions varies according to the ratio semen: sea water. 3. In very dense suspensions (d ≥ 5 x 109 sperm/ml.), the apparent low O2 uptake per unit quantity of spermatozoa is mainly due to inadequate O2 saturation of the lower layers of the suspension, in which the spermatozoa are virtually unable to respire. Such suspensions are not suitable for experiments in Warburg or Barcroft manometers. 4. In dense suspensions (4 x 108 < d ≤ 109 sperm/ml.) the Dilution Effect was observed when sea water was added to the suspension, in such proportions that the sperm density was only reduced by a factor of 1.14. No Dilution Effect occurred when isotonic ‘Analar’ NaCl was added in the same proportions. On the basis of the small dilution involved, and the negative results with ‘Analar’ NaCl, it is concluded that the Dilution Effect is not exclusively due to the sperm having more space to move after dilution and therefore being able to expend more energy. 5. The Dilution Effect occurs when isotonic ‘Analar’ NaCl containing 1 p.p.m. CuCl2 is added to a dense sperm suspension, in the above proportions. Stimulation of O2 uptake is proportional, over certain limits, to the amount of CuCl2 added. Both CuCl, ZnCl2, and to a lesser extent CuSO2, have similar effects. 6. In a particular experiment, egg-water and Cu salts were about equally efficacious in increasing the O2 uptake of a sperm suspension. 7. The characteristic decline in the O2 uptake of dense suspensions can be partly reversed by the addition of Cu salts. 8. In dilute suspensions (d < 4 x 108 sperm/ml.), there is no Dilution Effect when sea water or CuCl2 are added in the above proportions. On the other hand, the decline in O2 uptake can be partly arrested by the addition of Cu salts. 9. Diethyldithiocarbamate markedly inhibits the O2 uptake of unwashed sea-urchin spermatozoa diluted with sea water. The inhibition does not take place in the presence of added CuCl2. Cu may therefore have a catalytic function in the metabolism of sea-urchin semen. 10. The possibility that Cu lack is responsible for the reduced O2 uptake of spermatozoa in dense suspensions is considered.

The Respiration of Sea-Urchin Spermatozoa

1950 ◽  
Vol 27 (3) ◽  
pp. 420-436
Author(s):  
LORD ROTHSCHILD
Keyword(s):  
Oxygen Saturation ◽  
Sea Urchin ◽  
Seminal Plasma ◽  
Sea Water ◽  
Chelating Agent ◽  
Dilution Effect ◽  
O2 Uptake ◽  
Sperm Density ◽  
Dense Suspensions ◽  
Mammalian Spermatozoa

1. The O2 uptake of sea-urchin spermatozoa, Echinus esculentus, has been reexamined under varying conditions of sperm density, and in the presence of CuCl22H2O and sodium diethyldithiocarbamate (DDC). 2. The total O2 uptake of dilute sperm suspensions was previously thought to be higher than that of dense suspensions per unit quantity of spermatozoa (Dilution Effect I). This result is only obtained when the oxygen saturation of the dense suspension is inadequate, which may easily occur as the QOO2 of sea-urchin spermatozoa may reach 30 at 15.0° C. When oxygen saturation is satisfactory, the total O2 uptake of dense solutions is slightly greater than that of dilute ones. The experiment cannot be done in micro-respirometers of the normal Warburg type unless the density of spermatozoa per ml. suspension is less than about 109 corresponding to an initial semen dilution of 1:20 or 1:25. These figures apply to other manometric experiments on the O2 uptake of sea-urchin spermatozoa using normal amounts of material. 3. When movement ceases, there is a sharp increase in the O2 uptake of the suspension. 4. The addition of seminal plasma to dilute sperm suspensions does not inhibit the increased rate of O2 uptake, per unit quantity of spermatozoa, observed in these suspensions when compared with dense ones (Dilution Effect II). Dilution Effect II is therefore not caused by the dilution of an inhibitory substance in seminal plasma. 5. Sperm suspensions were prepared by diluting semen 1:50 with sea water and allowing them to respire for 45 mm. They were then centrifuged, the supernatant was discarded and the spermatozoa were re-suspended to different densities with sea water. This treatment has the following effects: (a) Centrifugation irreversibly damages the spermatozoa and reduces their O2 uptake. (b) Removal of the supernatant, which contains seminal plasma, and re-suspension in sea water also reduces O2 uptake. (c) The treatment markedly reduces Dilution Effect II. If the experiment is done in the same way but the suspensions are only allowed to respire for 10 min. before centrifugation, (a) and (b) are the same, but Dilution Effect II is normal. This shows that during metabolism, a regulatory substance is lost from dilute suspensions, as in mammalian spermatozoa; but this is not the cause of Dilution Effect II. 6. Dilution Effect II, considered as the reduced O2 uptake of dense suspensions, can be reversed by the addition of CuCl22H2O, 1 p.p.m., to the medium. 7. Dilution Effect II can be made to occur in sperm suspensions which do not normally exhibit it, by the addition of DDC, in concentrations as low as 3.64x10-5M (final concentration). The action of DDC is not greater when its concentration is increased to 10-3M, which suggests that in these conditions it acts as a chelating agent and not as a narcotic. For the same reasons its oxidation product, tetra ethyldithiocarbamyl disulphide, is unlikely to be responsible for DDC's inhibitory effect on sperm O2 uptake. 8. These results are consistent with the hypothesis that Dilution Effect II is due to the amounts of copper (or possibly zinc) in sea water being inadequate to satisfy the requirements of dense sea-urchin sperm suspensions. This situation is unlikely to arise during natural spawning as sperm densities are too low for the effect to occur in these conditions. Other interpretations of the stimulating action of copper and zinc are discussed. 9. The experiments remove several of the differences hitherto believed to exist between sea-urchin and mammalian spermatozoa.

Studies on the Respiration of Sea-Urchin Spermatozoa: III. Respiratory Quotient

1961 ◽  
Vol 38 (2) ◽  
pp. 249-257
Author(s):  
H. MOHRI ◽  
K. HORIUCHI
Keyword(s):  
Sea Urchin ◽  
Respiratory Quotient ◽  
Sea Water ◽  
Direct Method ◽  
O2 Uptake ◽  
Present Material ◽  
A Value ◽  
Sperm Suspension ◽  
Co2 Output ◽  
The Difference

1. The respiratory quotient of sea-urchin spermatozoa has been determined with Pseudocentrotus depressus, Anthocidaris crassispina and Hemicentrotus pulcherrimus. 2. The R.Q. of sea-urchin spermatozoa, measured by the Warburg direct method, has been reported to be near unity. This was also the case with the present material when the suspending medium was sea water, the R.Q. being 0.8-1.0. It was found, however, that the pH of sperm suspensions was markedly different in the presence and absence of alkali to absorb C02. 3. When the pH of the suspension was fixed by such buffers as 0.025 M-glycyl glycine, the R.Q. measured by the above method was about 0.7. This is in accord with the results of earlier metabolic studies, which indicated that endogenous phospholipids are the main substrates for the respiration of sea-urchin spermatozoa. 4. The O2 uptake of the present material, however, was found to be little affected by variation in pH. The difference in the R.Q. values obtained with ordinary sea water and buffered sea water, therefore, cannot be explained in terms of pH. 5. When the spermatozoa were suspended in ordinary sea water, the utilization of endogenous phospholipids was much reduced in the absence of alkali, while in buffered sea water the change in phospholipids was almost the same, with and without the absorption of CO2. 6. Determination of the R.Q. by the first method of Dickens & Šimer, in which the O2 uptake and the CO2 output were measured with one and the same sperm suspension, gave a value of about 0.7 with both ordinary and buffered sea water.

scholarly journals THE EFFECTS OF CAFFEINE ON OXYGEN CONSUMPTION AND CELL DIVISION IN THE FERTILIZED EGG OF THE SEA URCHIN, ARBACIA PUNCTULATA

1945 ◽  
Vol 29 (2) ◽  
pp. 63-72 ◽  
Author(s):  
Ralph Holt Cheney
Keyword(s):  
Cytochrome Oxidase ◽  
Sea Water ◽  
Direct Method ◽  
Relative Effect ◽  
O2 Consumption ◽  
O2 Uptake ◽  
Arbacia Punctulata ◽  
Normal Metabolism ◽  
Main Activity ◽  
Fertilized Egg

1. By means of the Warburg-Barcroft microrespirometer apparatus and the Warburg direct method, the relative effect of caffeine upon the O2 consumption of the fertilized egg of Arbacia punctulata was shown for the following concentrations in sea water: 0.002 per cent (M/10,000), 0.004 per cent (M/5,000), 0.02 per cent (M/1,000), 0.1 per cent (M/200), 0.2 per cent (M/100), 0.5 per cent (M/40), and 2 per cent (M/10). 2. In comparison with the normal eggs (uninhibited, non-caffeine-treated controls), caffeine in concentrations including and greater than 0.1 per cent (M/200) depressed the average uptake from approximately 25 to 61 per cent over the 3 hour period. In a number of instances, as typified by Experiment 10, the effective inhibitory concentration ranged from 0.02 per cent (M/1,000) upward and the degree of depression of the O2 consumption ranged from 10.6 per cent to 60.6 per cent. 3. All caffeine concentrations including and above 0.02 per cent (M/1,000) in the series used, resulted in decreasing the normal rate of cleavage division in the fertilized Arbacia eggs. 4. The higher concentrations (0.5 and 2 per cent) produced a complete blockage of the cleavage process. 5. Complete cleavage inhibition was noted only when the O2 uptake had been depressed to 50 per cent or more of the normal controls. 6. O2 consumption-time relationship data indicate an average depression, in O2 consumption over a 3 hour period, ranging from 25 per cent with a caffeine concentration of 0.1 per cent to a 61 per cent inhibition with a concentration of 2 per cent. 7. Concentrations of less than 0.1 per cent (certainly of less than 0.02 per cent) give variable results and indicate no significant effect. 8. It is inferred from the respiration data presented that it is probable that the inhibition of the O2 consumption in fertilized Arbacia eggs is due to the influence of caffeine upon the main (activity or primary) pathway. It will be observed that there are certain similarities of the caffeine data to the degree of inhibition accomplished by sodium cyanide. Moreover, it has been demonstrated that the cyanide probably acts on the cytochrome oxidase step in the cytochrome oxidase-cytochrome chain of reactions constituting the O2 uptake phase of respiratory metabolism. It is not improbable, therefore, that caffeine also may act upon the cytochrome oxidase enzyme. 9. From the viewpoint of environmental conditions influencing reproductive phenomena, it is of interest that caffeine can affect the normal metabolism of the zygote.

The Fertilization Reaction in the Sea-Urchin Egg

1949 ◽  
Vol 26 (2) ◽  
pp. 164-176
Author(s):  
LORD ROTHSCHILD ◽  
M. M. SWANN
Keyword(s):  
Light Scattering ◽  
Sea Urchin ◽  
Sea Water ◽  
Initial Increase ◽  
Point Of Entry ◽  
Sperm Suspension ◽  
Fertilization Membrane ◽  
A New Technique ◽  
Dark Ground ◽  
Cortical Change

1. After insemination of unfertilized eggs of Psammechinus miliaris and before the elevation of the fertilization membrane, a change in cortical structure is propagated over the egg surface or through the cytoplasm. When the fertilizing spermatozoon has become attached, the cortex progressively scatters more light when viewed under dark ground illumination. The cortex, which before fertilization is scarcely distinguishable from the cytoplasm, is white after the reaction is completed. 2. At 18° C. the change covers the egg surface in about 20 sec. 3. The conduction velocity is not uniform, there being a reduction in rate when the change is about halfway round the egg, after which there is a marked increase. 4. The cortex of the unfertilized egg shows a weak positive radial birefringence which disappears at the same time as the dark ground scattering appears. 5. Other changes in the egg structure occur at the same time, and are visible under dark ground illumination. These are: (a) a conical erection appears transiently at the site of sperm attachment; (b) the shape of the egg changes during the reaction; (c) there is a localized and transient decrease in light scattering at the point of entry of the spermatozoon, after the initial increase in cortical light scattering; (d) the fertilization membrane first appears at the point on the surface where the cortical change is initiated. 6. To investigate the possibility that the observed change might be the block to polyspermy, measurements were made of the speeds at which sea-urchin spermatozoa swim. A new technique has been evolved for this purpose. Spermatozoa were photographed under a special dark ground illumination system, with exposures of 0.25 sec. The heads of the spermatozoa trace out tracks on the film, the mean translatory speed being 190 µ/sec. The motion is helicoidal, the frequency of oscillation of the illuminated sperm heads being about 40/sec. 7. By treating the sperm suspension as an assembly of gas molecules, a rough estimate has been made of the frequency of collisions between the spermatozoa and an egg. For sperm densities of 105, 106 and 107/ml., and for the observed translatory sperm speeds, the number of collisions between spermatozoa and those parts of the egg surface unaffected by the propagated change, after it has been initiated, is 1.6, 16 and 160 respectively. 8. Some preliminary experiments on the insemination of oocytes have been carried out to assess the probability of a sperm-egg collision being successful. The results were: (a) oocytes react to insemination by the extrusion of blebs or papillae, each of which is associated with a spermatozoon; (b) this reaction is inhibited by insemination in Ca-free sea water and partially inhibited by acidified sea water. It is concluded that the extrusion of papillae represents an abortive fertilization reaction, the oocyte cortex being unable to propagate a block to polyspermy. The number of papillae extruded is less than the number of sperm-oocyte collisions. 9. The experiments on the insemination of oocytes favour the possibility that attachment of the spermatozoon to an egg is not followed by fertilization unless there exists a particular orientation, on a molecular scale, between the egg and sperm surfaces, and provided there has been no previous interaction between the spermatozoa and Gynogamone II. The low probability of fertilization that this implies is compatible with the hypothesis that the observed cortical change may be the block to polyspermy. Further experiments are needed to resolve this question.

The Physiology of Sea-Urchin Spermatozoa Action of Versene

1954 ◽  
Vol 31 (2) ◽  
pp. 252-259
Author(s):  
LORD ROTHSCHILD ◽  
A. TYLER
Keyword(s):  
Trace Metals ◽  
Sea Urchin ◽  
Seminal Plasma ◽  
Sea Water ◽  
Dilution Effect ◽  
Dense Suspension

1. The effect of adding sea water containing different concentrations of versene to suspensions of sea-urchin spermatozoa (Echinus esculentus) has been investigated, as regards their respiration, motility and fertilizing capacity. 2. The respiratory Dilution Effect is progressively reduced and finally abolished when, instead of sea water, sea water containing 10-6, 10-5, 10-4 or 10-3 M versene is added to sperm suspensions. 3. At the same time versene greatly delays the senescence of the spermatozoa, both as regards their motility and fertilizing capacity. For example, after seventeen hours, a 105 sperm/ml. suspension in sea water containing 10-3 M versene has 125 times the fertilizing capacity of a suspension containing 107 sperm/ml. without versene. 4. The change in the ratio of seminal plasma to sea water which occurs when a dense suspension is diluted does not explain the Dilution Effect. 5. These results are discussed in relation to the hypothesis which accounts for the Dilution Effect in terms of trace metals, particularly copper, normally occurring in sea water, and the amounts available per spermatozoon under various conditions of dilution.

The Physiology of Echinus Esculentus Spermatozoa

1948 ◽  
Vol 25 (1) ◽  
pp. 15-21
Author(s):  
LORD ROTHSCHILD
Keyword(s):  
Sea Urchin ◽  
Sea Water ◽  
O2 Uptake ◽  
Reversible Effect ◽  
Spectroscopic Examination

1. The O2 uptake of Echinus esculentus sperm suspensions is strongly inhibited by CO. In equilibrium with a mixture of 90% CO and 10% O2, the O2 uptake is 60% less than that of an identical suspension in equilibrium with 90% N2 and 10% O2. 2. This inhibition is completely reversed by light. 3. Spectroscopic examination revealed cytochromes a, a3, b and c. On treatment with CO the spectrum of COa3 was observed. 4. These results establish that the cytochrome system is the catalytic agent which controls the respiration of sea-urchin spermatozoa. 5. The O2 uptake of sperm suspensions in equilibrium with 90% N2 and 10% O2 is about 10% lower than in air. 6. Certain difficulties in measuring the R.Q. of sperm are discussed. 7. The reversible effect of CO on the O2 uptake of spermatozoa is the same whether they are in egg water or sea water.

The Fertilization Reaction in the Sea-Urchin

1953 ◽  
Vol 30 (1) ◽  
pp. 57-67
Author(s):  
LORD ROTHSCHILD
Keyword(s):  
Sea Urchin ◽  
Sea Water ◽  
Interaction Time ◽  
Conduction Time ◽  
Incomplete Block ◽  
O2 Uptake ◽  
Sharp Reduction ◽  
Sea Urchin Eggs

1. Treatment of unfertilized sea-urchin eggs with sea water containing nicotine is known to induce polyspermy when the eggs are subsequently inseminated with homologous spermatozoa, at densities which cause a very small amount of polyspermy in untreated eggs. 2. If nicotine were to increase the speeds at which sea-urchin spermatozoa swim, the chances of fertilization, and therefore of polyspermy, might be increased. Nicotine does not increase sperm speeds; in addition, it causes a sharp reduction in the O2 uptake of these spermatozoa. 3. The only other ways in which nicotine could induce polyspermy are by altering the egg surface in such a way that the probability of fertilization is increased by a factor of about twenty; or by lengthening the conduction time of the block to polyspermy. Experiments described in this paper show that the first explanation is untenable and therefore that the second is the correct one. It is concluded that nicotine abolishes the fast incomplete block to polyspermy and that over-exposure to this substance probably abolishes the block to polyspermy altogether. 4. Polyspermic eggs divide sooner than monospermic ones. 5. When, as in these experiments, eggs are allowed to interact with spermatozoa for known times, and then functionally separated by immersion in hypotonic sea water, some eggs, presumably those which sustain a successful sperm-egg collision at the end of the interaction time, are activated but not fertilized by the spermatozoon, as in the pseudogamous nematodes. Cleavage does not occur though the egg nucleus swells. 6. Previous results in the same field and observations by other workers are discussed.

Studies on the Respiration of Sea-Urchin Spermatozoa

1963 ◽  
Vol 40 (4) ◽  
pp. 573-586
Author(s):  
H. MOHRI ◽  
I. YASUMASU
Keyword(s):  
Sea Urchin ◽  
Sea Water ◽  
Platinum Electrode ◽  
Paracentrotus Lividus ◽  
Inhibitory Effect ◽  
O2 Uptake ◽  
Partial Pressures ◽  
Ph Variations ◽  
Hemicentrotus Pulcherrimus

1. The effect of PCOCO2 on the respiration and motility of sea-urchin spermatozoa was studied on Anthocidaris crassispina. Some points were also corroborated on Hemicentrotus pulcherrimus, Pseudocentrotus depressus, Paracentrotus lividus and Sphaerechinus granularis. 2. It was found that any level of CO2 above 1%, both in oxygen and in air, inhibited the O2 uptake of spermatozoa suspended in sea water, measured polarographically with a vibrating platinum electrode. The inhibitory effect paralleled the PCOCO2 and was completely reversed by introducing oxygen or air. 3. pH variations between 8.50 and 6.75 had no influence on O2 uptake, when the pH was stabilized with 0.05 Mhistidine-HCl-NaOH. O2 uptake was, however, reduced to some extent outside this range, especially on the acid side. Although the increase in PCOCO2 is inevitably followed by a decrease in pH, the inhibitory effect of CO2 far exceeds that caused by the reduction in pH. 4. The O2 uptake rate was little affected by the addition of both bicarbonate and carbonate ions to the suspending medium, although the former had a slightly stimulating effect at certain concentrations. 5. In buffered sea water, CO2 had little influence on O2 uptake even at partial pressures as high as 10% which inhibited the bulk of O2 uptake in sea water. 6. Sperm motility was also inhibited by CO2. In this case, too, the inhibition paralleled the PCOMCOM2 and was completely reversible. The effect was more pronounced in air than in oxygen, and in dense sperm suspensions than in dilute ones. 7. These results suggest that gaseous CO2 is the factor responsible for the inhibitory effect. The possible role of CO2 in the dilution phenomena of sea-urchin spermatozoa is discussed.

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