Marchal points out the analogy of this phenomenon to the artificial polyembryony that has been induced in Echinoderm and other eggs by separating the blastomeres, and suggests that the abundant food-supply afforded by the host-larva is favourable for this multiplication of embryos, which may be, in the first instance, incited by the abnormal osmotic pressure on the egg.
The dissociation theory was originally suggested by the osmotic pressure relations.
According to the investigations of Svante Arrhenius the osmotic pressure in atmospheres may be obtained by simply multiplying the temp rature of freezing (r) by the factor -12.08, and it varies with temperature (t) according to the law which holds good for gaseous pressure.
Thus, while increased pressure in the blood or lymph vessels may be one factor, and increased permeability of the capillary endothelium another, increased osmotic pressure in the tissues and lymph is probably the most important in the production of dropsy.
Hence the osmotic pressure is measured by the work done per unit change of volume of the solution.
There must, then, be a relation between the rate of change of the concentration and the osmotic pressure gradient, and thus we may consider the osmotic pressure gradient as a force driving the solute through a viscous medium.
Frazer, who have made direct measurements of osmotic pressure of solution of cane-sugar, have also measured the freezing points of corresponding solutions.
To investigate the osmotic pressure of a' strong solution we may consider the hydrostatic pressure required to increase its vapour pressure to an equality with that of the solvent.
The reasoning given above is independent of the temperature, so that the variation with temperature of the osmotic pressure of a dilute solution must be the same as that of a gas, while Boyle's law must equally apply to both systems. Experimental evidence confirms these results, and extends them to the cases of non-volatile solutes - as is, indeed, to be expected, since volatility is merely a matter of degree.
Much more important is the effect of the alteration in the amount of crystalloids in the tissues and blood and therefore of the alteration in the osmotic pressure between these.