If we analyze the Sputa we find fibrin and even lung muscle.
"Philosophy of Osteopathy"
Andrew T. Still
The germ of pulmonary consumption, known as the bacillus tuberculosis, is contained in the breath and the Sputa from the lungs of its victims.
"A Practical Physiology"
Albert F. Blaisdell
It appears, from the connection, to have been a very unclassical word, whimsically derived by the author of it from Sputa, spittle.
"Cicero's Brutus or History of Famous Orators; also His Orator, or Accomplished Speaker."
Cicero