(1) Save as hereinafter provided in this section, it shall be no defence in a prosecution under this Chapter to prove merely that the accused was ignorant of the nature, substance or quality of the drug 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 purpose of test or analysis, has not been prejudiced by the sale.
(2) For the purposes of section 18 a drug shall not be deemed to be misbranded or 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 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 or cosmetic or to conceal its inferior quality or other defects; or
(b) in the process of manufacture, preparation or conveyance some extraneous substance has unavoidably become intermixed with it; provided that this clause shall not apply in relation to any sale or distribution of the drug or cosmetic occurring after the vendor or distributor became aware of such intermixture.
(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.