Introduction

Sir, congratulations on your leading article Degrees of separation published on 26 January. I enjoyed reading it immensely.

However, my main concern in this letter is the cover image that was published in the journal on 12 January 2008 (Vol. 204, No. 1). The image has been described incorrectly in the caption/legend.

The last sentence of the legend states: 'The tooth is covered by a coat of white enamel (dark purple), the hardest tissue in the human body'.

The tissue referred to as white enamel is, in fact, cement or cementum. Outside the cement is the periodontal ligament, the latter being connected to the bone. The section shown was cut through the root of a tooth, not through the crown. There is no enamel anywhere in the picture. Enamel is found in the crown of a tooth.

I am sure you will appreciate that this is a very fundamental point. It is a shame to see such a poor description in the journal.