As astonishing and untouchable today as it was when it first came out in 1966, the 13-minute title track ignited the whole '60s movement towards guitar improvisation — and that, if you are unfair enough to do so, is about the only bad thing you could say about it.

Their second album expanded on the integrated Chicago band’s already-proven mastery of blues by taking up guitarist Michael Bloomfield’s growing fascination with Indian ragas, creating an unprecedented fusion that provided the earthy cornerstone to cerebral psychedelia. The 8-minute version of Cannonball Adderly‘s “Work Song” explores the inseparability of jazz and blues. The rest of the set offers some inspired takes on blues styles and variants (plus a Monkees song!), led by the leader’s hard-edged vocals and singular, single-note harmonica style and the guitar interplay between Bloomfield and Elvin Bishop. Anchoring it all are drummer Sam Lay and bassist Jerome Arnold, who Butter hired away from Howlin’ Wolf. They gel on tuff tracks like “Two Trains Running” to create a sound as down-to-earth as “East-West” is soaring-skyward.