This means that, with individual exceptions, creditors generally gain and debtors lose by falling prices.
But this is fully true only in respect to loans already made.

For just to the extent that such a movement of prices comes to be more or less regularly in the same direction, both borrowers and lenders are able to take it into account, and as experience shows, do take it into account.[13] When prices fall men become more eager to sell wealth, to lend the proceeds, and more reluctant to borrow for investment at the prevailing rate of interest and at the prevailing prices.

There is an incentive to divest one's self of ownership (e.g., by selling stocks) and to become a lender (e.g., by buying bonds).

This whole situation is reversed in a period of rising prices.

The result is that the rate of interest in any long continued period of falling prices (such as from 1873 to 1896) has a trend downward and in a period of rising prices (such as from 1897 to 1915) has a trend upward.