You are most likely describing a sebaceous cyst. These can be found anywhere on the body but seem to favor the area along the back. If you're lucky, this may respond favorably to repeated warm compresses. If the thick substance doesn't stop coming out, then you need to have a veterinarian take a look at it for further treatment. They might be able to cauterize it or may have to surgically remove it. The worst thing you could do is to keep squeezing it--that will only make it be more inflamed and likely to get infected.
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