It may be concluded that 3-keto-2:3-dihydrobenz-1:4-thiazine and its derivatives, with the exception
of the unsubstituted compound itself and
the 6-nitroso-derivative both of which have a
slight stimulant effect, have no effect on the
'intermediate' preparations of Ascaris.
All but six, namely the 6-arsonic and stibonic
acids, the 6-mercuric chloride compound, the 6-amino compound coupled with phloroglucinol and salicylic acid, and 6:6'-bis-(3-keto-2:3-dihydrobenz-1:4-thiazine), have a paralysant effect on liver fluke,
the 6-amino and 6-thiol compounds being almost
lethal at a concentration of 1 in 1000.
We may, therefore, conclude that certain atoms
or groups increase the activity, whilst others decrease
the activity of 3-keto-2:3-dihydrobenz-1:4-thiazinne towards liver fluke. The inactivity towards
Ascaris may be partly due to the inability
of the compounds to penetrate the Ascaris cuticle,
a difficulty which it might be possible to overcome
by using a suitable wetting agent.