Left-handed subunit helix in flagellar microtubules

Abstract

ONE of the problems encountered in the study of a small negatively stained biological object by electron microscopy concerns the uncertainty in the distribution of stain around the object. If the particle is considered broadly as having two ‘sides’ one in contact with the support film and the other not, then the staining conditions may produce an image which represents one or other of the two surfaces or both sides together. Generally, the degree of contrast lies somewhere between these extreme cases¹. Unless there is a differential staining of one side with respect to the other and an unambiguous distinction between the near and far sides can be made it is generally impossible to determine the right or left-handedness of an object. (Moody² has however been able to demonstrate the right-handed sense of bacteriophage T4 sheath by the use of a convenient staining artefact).