(after stating the facts). One of the assignments of error is that the court erred in instructing the jury. The court told the jury that the undisputed evidence showed that Brunson was indebted to Hooks in the sum of $37.50, and that the only question for them to decide was whether or not it was understood by both parties that Hooks should retain the title to the mule until the $37.50 was paid.

The court instructed the jury that the burden of proof was on Hooks. The court also instructed the jury that, if the mule was traded merely on an agreement with Brunson to pay the sum of $37.50 without any reservation of title in Hooks, the latter was not entitled to recover the mule.

The instructions given were correct. The evidence of both parties to this lawsuit shows that Brunson agreed to pay Hooks $37.50 as the difference when he traded another mule for the mule in question, and that he has not paid that amount to Hooks. Hence there was no error in telling the jury that the evidence on this point was undisputed.

The point in dispute between the parties was whether or not Hooks retained title to the mule in question until the $37.50 was paid, and this question was submitted to the jury under proper instructions.

It is true that Brunson had mortgaged the mule he traded to Hooks, but this did not make any difference, for two reasons. In the first place, he received permission from the Tobin Mercantile Company to trade the mule, and in the second place, the title to that mule is not involved in this suit. The title to the mule which Hooks traded to Brunson alone is involved in this lawsuit.

As between the Tobin Mercantile Company and Brunson, the agreement that the mule traded for should be substituted for the one already included in the mortgage was a valid and binding contract.

In Howell v. Walker, 111 Ark. 362, it was held that an agreement for substitution in a chattel mortgage is valid in equity between the parties, under the maxim that equity treats that as done which the parties intended to be done.

Hooks was not a party to this agreement, and it had no effect whatever on his rights in the premises. He had title to the mule he traded to Brunson, and under numerous decisions of this court he had a right to retain the title to his own property until he was paid therefor.

The jury by its verdict found that Hooks retained the title to the mule he traded to Brunson until the $37.50 balance due on the purchase- price was paid. When Brunson turned the mule over to the Tobin Mercantile Company in part payment of his mortgage indebtedness and failed to pay Hooks, as he had agreed to do, the latter had a right to replevin the mule. The Tobin Mercantile Company sold the mule to J. J. Whittington, who claimed the same at the time the present suit was instituted. Therefore it was not necessary for the plaintiff to make demand for the mule before bringing the suit. Sibeck v. McTiernan, 94 Ark. 1.

It follows that the judgment must be affirmed.