LECTURE V, 
SCLEROGEN. 
I now proceed to speak of another kind of deposit in 
cells, which still retains the name of sclerogen , originally 
given it by Turpin ; this deposition always takes place 
in the interior of the cell, but rarely if ever completely 
fills it, a central cavity, and certain radiating tubes or 
canaliculi being left at intervals in the deposit. In the 
Histological Catalogue of the Museum of the College of 
Surgeons, all the principal varieties of the deposit of 
sclerogen , are classified and described under the name 
of Hard tissues, and contrasted with bone and teeth, 
which form the hard tissues of animals. Those who 
are in the habit of eating Pears will remember, that 
near the centre of the fruit, and in the neighbourhood 
of the seeds, there is something which grates between 
the teeth : it is known to botanists as the Gritty tissue, 
