my black & white 'tuxedo' jellicoe is now approaching 19; his 'stools' are runny & black. once a day. the Vet told me to give him laxatives in his meals and...to feed him only the pate type of food [i give him a joint supplement once a day; he has difficulty jumping up onto the couch]. i also give him bits of smoked salmon in an attempt to supply him with Omega-e. he no longer grooms & cannot retract his nails (i have given him a bath lately - he has dandruff); i trim his nails. he still uses the litter successfully; he sleeps most of the time; his eyes are clouded; he's increasingly eating - rather hefty now; he doesn't cry or yowl & doesn't seem to be 'lost'. do the stools mean he has cancer? is he in pain? i hesitate to put him down if i don't have to. any advice would be warmly appreciated. [his sister died at 17 so i brought a new kitty into the house; she's 2 years; they get along well for the most part altho' she keeps wanting him to play]. they are both indoor cats. thanks!