Provers should be chosen from humans, both male and female, old and young; animals. male and female, old and young; and plants of different kind.

Tabacum and Sabadilla each produce a characteristic yet different effect upon smooth muscles; that a mixture of the two drugs also produces a definite effect yet totally different from that obtained from using either remedy alone.

If we know the sequence of symptoms in the order of their appearance, we can more speedily and accurately compare the symptoms of the prover and patient, after having taken the case.

Pure mental symptoms are rarely found. Brain symptoms are very frequently found in combination with those of some other tissue or organ.