Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 94, § 194A

In any prosecution in which it is alleged that the defendant for pay or otherwise delivered or offered to deliver to any person shellfish which are adulterated within the meaning of clause sixth of section one hundred and eighty-six, or however otherwise the offence may be described, it shall be a defense if the defendant shows that such shellfish were taken from an area not designated as contaminated by the department of public health or have passed a shellfish treatment plant approved by said department unless it appears from all the evidence that he knew or ought to have known of such adulteration or that he caused or contributed to the same.