When one without fault himself is attacked by another in such a manner or under such circumstances as to furnish reasonable grounds for apprehending a design to take away his life, or do him some great bodily harm, and there is reasonable ground to believe the danger is imminent and that such design will be accomplished, and the person assaulted has reasonable ground to believe and does believe such danger is imminent, he may act upon such appearance and, without retreating, use such force as is necessary against his assailant if he has reasonable ground to believe and does believe that such force is necessary in order to avoid the apparent danger. A killing under such circumstances is excusable, although it may afterwards turn out that the appearances were false and that there was, in fact, neither design to do him serious injury or danger that it would be done. But of all this the jury must judge from all the evidence and circumstances of the case.