The water content of epididymal bull spermatozoa in media of osmolalities corresponding to those of seminal plasma and to the fluids from the cauda epididymidis was determined by a gravimetricvolumetric method as 0·586 ± 0·0052 and 0·512 ±0·0086 ml per ml of cells, respectively. It was related to the ionic concentrations in mmol/ litre of spermatozoa determined by the conversion of the mean values of the major cations expressed as mequiv./litre, mg/100 g, or mg/100 ml, established by previous authors. The osmolalities of the intracellular fluids were also calculated. They were compared with the osmolalities of the extracellular fluids, the comparison making it possible to perform an introductory analysis of the osmotic-equilibrium states of bull spermatozoa.
The calculated osmolality of the cytosol of epididymal spermatozoa was found to be about 40 mosmol less than that of the epididymal fluids. This discrepancy from the state of osmotic equilibrium is not serious when considering the errors, which are probably inherent in the values of both the ion and water-content determinations. The osmolality of the cytosol of ejaculated spermatozoa was calculated as 1·7 times greater than that established for seminal plasma. If the calculated value is reasonably correct, this should imply that, for the existence of identical concentrations of osmotically active particles on both sides of the cell membrane of spermatozoa suspended in seminal plasma, a fraction of the intracellular ions, amounting to about 38%, must be assumed to be 'bound'.
Determinations of the water-content of the spermatozoa furnished data from which it was possible to calculate the specific gravity of the cells. This was compared with those actually established by gradient centrifugation in various media by different authors.
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