As the blood, etc. is dried by now, have you tried to slap the trousers to get the dried goo out? I too wear wool surplus trousers but only get a little whitetail blood on them, which has come off once dried. I have rubbed snow on the blooded areas at times to remove blood or lessen the amount of blood. If you now have a stain rather than dried material, I am not sure what might work. But, don't throw those surplus wool trousers away!