Dear Mr. Darwin,

I have examined the three bits you have been kind enough to send me;¹ this is the result of my examination: In N^o. 2 there was extremely little de-calcified of the enamal, of the dentine only that part that is nearest to the free edge of the preparation and farthest away from the enamel. In N^o. 3 a great deal of enamel decalcified, of dentine the greater part. In N^o. 8 there was less than half of the enamel de-calcified and appearently also less than in N^o. 3, but the greater part of the dentine.

In general the enamel is most de-calcified at the edge, whence tracts of de-calcified tissue extend towards the depth of the enamel; the dentine is best de-calsified nearest to the edge and where it is thinnest.

The structure of both the enamel and the dentine is in no way altered.²

The examined bits were taken from a canine tooth of a dog.

I have asked D^r. Sanderson as regards the action of gastric juice on tooth-substance and he told me he is going to make the necessary experiments.³

Bones of the skull of a cat subjected to artificial digestion for about a week, about which, as I suppose, D^r. Sanderson has already written to you, were seen to be de-calcified and to become broken up into their lamellae and fragments of very minute size, up to such small fragments just visible for the naked eye. The larger lamellae were completely or partially cracked, each such territory comprising a greater or smaller number of Haversian systems of bone lamellae. In those fragments that were large enough to be examined microscopically there was no structural change, except that I fancy that at the edges of the fragments the bone matrix appeared to be rarified, thus producing the appearance as if the canaliculi of the bone corpuscles had become larger. Otherwise the bone corpuscles and their canaliculi were very distinct.⁴

Taking the liberty of saying that it gives me the greatest pleasure if I can assist you in any way, | I am, dear Sir, yours | very sincerely | E. Klein.