of potassium nitrate; these three fluids being all ãisotonicã with one another. As we alter the concentration of potassium nitrate, the cell assumes certain definite forms corôÙreôÙsponôÙding to definite concentrations of the salt; and, as a further and final proof that the phenomenon is entirely physical, it is found that other salts produce an identical effect when their concentration is proportionate to their molecular weight, and whatever identical effect is produced by various salts in their respective concentrations, a similarly identical effect is produced when these concentrations are doubled or otherwise proportionately changed59.
Thus the following table shews the percentage concentrations of certain salts necessary to bring the cell into the forms a and c of Fig. 95; in each case the quantities are proportional to the molecular weights, and in each case twice the quantity is necessary to produce the effect of Fig. 95c compared with that which gives rise to the all but spherical form of Fig. 95a. {275}
| % concentration of salts in which the sperm-cell of Inachus assumes the form of | ||
|---|---|---|
| fig.ô a | fig.ô c | |
| Sodium chloride | 0ôñ6ã | 1ôñ2 |
| Sodium nitrate | 0ôñ85 | 1ôñ7 |
| Potassium nitrate | 1ôñ0ã | 2ôñ0 |
| Acetic acid | 2ôñ2ã | 4ôñ5 |
| Cane sugar | 5ôñ0ã | 10ôñ0 |
If we look then, upon the spherical form of the cell as its true condition of symmetry and of equiôÙlibôÙrium, we see that what we call its normal appearance is just one of many intermediate phases of shrinkage, brought about by the abstraction of fluid from its interior as the result of an osmotic pressure greater outside than inside the cell, and where the shrinkage of volume is not kept pace with by a contraction of the surface-area. In the case of the blood-corpuscle,