216 RAINEY, ON DENTAL TISSUES. 
progress of formation of all the so-called “ dentinal tubules,” 
a portion of dusty-looking material—incipient dentine— 
always intervenes between the partially formed tubules and 
the dental pulp, all the fluid which is contained in their 
interior, must have first passed through mere interstices 
or spaces. Hence if at this, the most important epoch of a 
tooth’s formation, mere spaces have sufficed for the con- 
veyance and supply of interstitial fluid to its substance, I 
do not see why parietes should be afterwards added to those 
spaces; as by such an addition a complex form of structure 
would be superadded to a simple one, after the tooth-tissues 
had ceased to perform any obvious organic function, their 
office being purely mechanical; and thus this substitu- 
tion of tubes with parietes for mere spaces would come 
too late to serve any obvious purpose. In other parts where 
tubes exist, as in the tracheze of insects, or ducts of glandular 
organs, a function is performed entirely distinct from that 
which was required to build up these parts—and one obviously 
requiring such a system of tubules. But the spaces between 
the dentine-fibres and between the dentine-globules do not 
come under this category, but appear to be merely a form of 
interstice, suited to the character and form of the tissue in 
which they exist, and so to be strictly analogous to the spaces 
between the rods of enamel. 
As respects the proofs resting upon facts apparent from the 
examination of dentine by the microscope, I am convinced 
they are sufficient to satisfy any one who will examine the 
subject with impartiality. It may not be out of place here 
to state that the microscopic examination of the dental tissues 
is far more easy than is generally supposed. For the 
successful investigation of this subject foetal teeth, perfectly 
fresh, are indispensably necessary, and these can be obtained 
almost at any time. I have especially examined those of the 
calf as being most easily procurable. It will not be necessary 
that the investigator should grind and polish sections of all 
the teeth which he examines; however, it will be advisable 
that he should possess two perfect sections, which can be 
easily procured from the opticians. I make these remarks 
rather to encourage those who are afraid to undertake the 
subject from the supposed difficulty of making suitable pre- 
parations, than to dissuade any one from using his own fingers. 
Sections of decalcified dentine, examined in glycerine, are 
very useful, and can be made without any difficulty. It has 
been stated, that even and regular sections cannot be made of 
teeth softened by an acid. This does not in the least agree 
with my experience. A very convenient way of decalcifying 
