The priests had built up a great complex of forms, where at every turn fees were demanded.

The whole expense, falling on the one individual to whose benefit accrued the sacrifice, must have been enormous; in the case of ordinary people impossible.

But the priests then permitted the sacrifice of substitutes, for their fees still remained; and even in the case of human sacrifice some such caution may have worked, for ordinarily it cost 'one thousand cattle' to buy a man to be sacrificed.

A proof of this lies in the fact that animal sacrifices were not forbidden at any time, only smaller (cheaper) animals took the place of cattle.

In the completed Brahmanic code the rule is that animals ought not to be killed except at sacrifice, and practically the smaller creatures were substituted for cattle, just as the latter had gradually taken the place of the old horse (and man) sacrifice.
If advancing civilization results in an agreeable change of morality in many regards, it is yet accompanied with wretched traits in others.
The whole silliness of superstition exceeds belief.