I hunted elk again in 2014, killed a cow elk, and filthed another pair of these M-51 wool trousers. I ran water over the dirty spots on the trousers (the seat as well as the knees and the cuffs) while I rubbed the cloth against itself to free the dried blood and probably gutting material. I squeezed the water out of the material, watching the water run rusty red. I kept doing this until the water ran clear. Then I washed the trousers in the clothes washer using COLD water on a DELICATE cycle using WOOLITE soap. The pants came out acceptably clean. Plenty clean enough for elk hunting.
I then did the same processing on the pair of M-51 wool pants that had not come clean back in 2011. It looks like I will have similar results with them. I'm very pleased with the results. These are great hunting pants.