It's possible that Bourse has an anal gland problem and may be licking excessively at his bottom, because it's uncomfortable. Anal glands can become impacted, infected or even rupture if they are full and not expressed (emptied) by the vet. Here is more information:
If his stools are small and dark, he may be having a problem with slight constipation and you can help that by encouraging him to drink more (a cat drinking fountain is great) and give him some hairball gel like Laxatone or Petromalt, according to the directions on the product.
If they're very dark, like 'tarry/black,' this could indicate some bleeding in his upper digestive system, and this should be checked out by his vet. His bottom should also be looked at in person, to diagnose the problem and have it treated so he feels more comfortable.
Cats generally hate baths, so if you could just gently wipe the area clean with a non-alcohol baby wipe or cat cleansing cloth, that should be good for the skin and the fur that is also soiled.
The small while balls may be part of the irritation from an anal glad problem, if there is one, but in any case, his vet would need to evaluate this condition and then, treat it. If the small white balls are moving, they are intestinal parasites of some sort.
If he is overweight, changing to a high quality canned food might be healthier, because it contains less carbohydrates. Also, portion control is important, so feed him smaller portions several times a day. A grain-free food is recommended: Wellness, Wellness CORE, EVO, Blue, and many others are available in both canned and dry, at your pet supply stores.
I know he hates anyone touching his bum, but, if you're able, for now, try to apply a small film of plain Neosporin ointment (not with 'pain relief') on the area, to soothe it. It's not harmful if he licks it off.
Try to have him seen as soon as you can, so you know the cause of this problem and then treatment can be prescribed.
I hope all will be well with Bourse!
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