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From the Lifshitz theory, Hamaker coefficients have been computed for all the monoglyceride-alkane thin films in polar liquids described in the previous two parts of this paper. The calculations have been based on three different models of the films. The first model represents the film simply as an isotropic layer of liquid hydrocarbon, in which it is assumed that the lipid and solvent chains are intimately mixed. The second is similar to the first except that it includes two 0.4 nm layers of glycerol to represent the glyceride polar groups of the lipid. The theoretical Hamaker coefficients for these two models are identical to withinca. 10% and, for twelve out of the twenty-four systems examined, they agree to withinca. 20 % with the corresponding experimental coefficients. In the remaining systems, which mainly involve very thin films, the theoretical and experimental results differ by as much as a factor of three. In seeking an explanation for these discrepancies, calculations were carried out for the third model in which, instead of assuming complete mixing of the lipid and solvent chains, it is assumed that they are completely segregated. The hydrocarbon layer is thus split into three layers, i. e. lipid chains–alkane solvent–lipid chains. As with the first and second models, for about half the systems, theory and experiment agree to within 20 % but, for the remaining films, the third model is a considerable improvement as it yields no discrepancies with the experimental data greater than a factor of two. Such discrepancies as do still exist may be accounted for by recognizing thatsomesolvent must in­evitably be present in the lipid chain regions and that, in fact, the state of the interior of a film is intermediate to those assumed in the second and third models. The results exemplify well how successful the Lifshitz theory can be in liquid systems, but they also emphasize the very large effects which small differences in dielectric properties can have on the van der Waals forces in thin films.

Carnitine and glycerylphosphorylcholine, two well-known constituents of the mammalian epididymis, are shown to be equally characteristic of another sperm-storing organ, namely the spermatophore of a cephalopod mollusc, Octopus dofleini martini .

The spermatozoa of the giant octopus of the North Pacific, freshly removed from spermatophores, showed very little motility, but on dilution with sea-water or 2.7% NaCl, followed by dialysis against either of these two media, they became intensely motile and remained so for several days at 2 to 10 degrees C. At higher temperatures, particularly above 25 degrees C, octopus spermatozoa lost their motility rapidly. At 35 degrees C, complete and irreversible loss of motility occurred within less than 1 min. The motility of octopus spermatozoa at 2 to 10 degrees C persisted under both anaerobic and aerobic conditions and did not require the presence of exogenous glycolysable sugar. The addition of spermatophoric plasma to a motile sperm suspension inhibited motility. Other inhibitors were sodium azide, 2,4-dinitrophenol and ethylenediaminetetra-acetate, at 0.001 M concentrations. ATP, ADP and arginine phosphate have been identified and quantitatively measured in octopus spermatozoa. On prolonged incubation of motile sperm suspensions at 3 degrees C, ATP and ADP did not decline appreciably, whilst arginine phosphate decreased considerably. The decrease was even more pronounced in sperm suspensions which had first been inactivated by short exposure to 35 degrees C, prior to prolonged incubation at 3 degrees C. Glycogen, the main carbohydrate store of octopus spermatozoa, remained at a high concentration even in sperm suspensions kept for 5 days at 3 degrees C, and there was no appreciable difference in that respect between a sample containing motile spermatozoa and one in which, at the outset of incubation, the spermatozoa were immobilized by heating to 35 degrees C.