(1)Save as hereinafter provided in this section, it shall be no defence in a pro - secution under this Chapter to prove merely that the accused was ignorant of the nature, substance or quality of the drug 4[or cosmetic] in respect of which the offence has been committed or of the circumstances of its manufacture or import, or that a purchaser, having bought only for the pu rpose of test or analysis, has not been prejudiced by the sale.
(2)5[For the purposes of section 18 a drug shall not be deemed to be misbranded or 6[adulterated or spurious] or to be below standard quality nor shall a cosmetic be deemed to be misbranded or to be below standard quality] only by reason of the fact that —
(a)there has been added thereto some innocuous substance or ingredient because the same is required for the manufacture or preparation of the drug 4[or cosmetic] as an article of commerce in a state fit for carriage or consumption, and not to increase the bulk, weight or measure of the drug 4[or cosmetic] or to conceal its inferior quality or other defects; or
7* * * * *
(b)in the process of manufacture, preparation or conveyance some extraneous sub stance has unavoidably become intermixed with it: provided that this clause shall not apply in relation to any sale or distribution of the drug 4[or cosmetic] occurring after the vendor or distributor became aware of such intermixture.
8[(3) A person, not being the manufacturer of a drug or cosmetic or his agent for the distribution thereof, shall not be liable for a contravention of section 18 if he proves—
(a)that he acquired the drug or cosmetic from a duly licensed manufacturer, distributor or dealer thereof;
(b)that he did not know and could not, with reasonable diligence, have ascertained that the drug or cosmetic in any way contravened the provisions of that section; and
(c)that the drug or cosmetic, while in his possession, was properly stored and remained in the same state as when he acquired it.]