As with all magical writings of this nature, the metal-bound Manual of Bodily Health appears to be an arcane, rare, but non-magical book. 

If a detect magic spell is cast upon it, the manual' will radiate an aura of magic. 

Any single character who reads the work (24 hours of time over 3-5 days) will know how to increase his or her Constitution by 1 point by following a regimen of special dietary intake and breathing exercises over a 1 month period. 

The book disappears immediately upon completion of its contents. 

The 1 point of Constitution is gained only after the prescribed regimen is followed. In 3 months the knowledge of the secrets to bodily health will be forgotten. The knowledge cannot be articulated or recorded by the reader. 

The manual' will not be useful to any character a second time, nor will other than a single character be able to benefit from it.

Special Note. All magical books, librams, manuals, tomes, etc. appear to be "normal" works of arcane lore. Each is completely indistinguishable from the other by visual examination of the outer parts or by detection for magic aura. 

Bard characters will have normal chances of finding out the nature of such writings, as will an identify spell from a magic-user. 

Otherwise, only a wish will be useful in typing a magical writing, i.e. alter reality, commune, contact higher planes, limited wish, true seeing, true sight, and other spells or powers are useless. 

A wish will reveal general contents of a book, telling what characteristics or class is most affected (not necessarily benefited) by the work. It requires a second wish to determine exact contents. 

After being perused by a character, most of these magical works will vanish forever, but those which are non-beneficial to the reader will typically be attached to the character, and he or she will be unable to be rid of it. 

If the work benefits another alignment of character, the possessor is geased to conceal and guard the writing. 

As Dungeon Master you should use your judgment and imagination as to exactly how these items will be treated, using the rules herein as parameters.