Oscar Wilde questions

I was wondering about the specific meaning of two words which Oscar Wilde uses in his Preface to "The picture of Dorian Gray". One is "morbid", in the sentence: "No artist is ever morbid. The artist can express everything."

The other is "all" in sentences like: "All art is at once surface and symbol" or "All art is quite useless". Do you think he means "all arts are." (every art is.) or perhaps ("art is always.")?

Thanks a lot!

Ruth