1887.] MICROSCOPICAL JOURNAL: Vie 
bow] was filled with ice and covered with a glass plate. This was levelled, 
and the plate to receive the gelatin was laid upon it. The gelatin was warmed 
by placing the test-tube in warm water and: then poured upon the plates and 
evenly spread with a copper wire that had been heated in the flame of a spirit- 
lamp. The plates were successively cooled, each being protected from dust 
by a dish-cover, and in a few minutes the gelatin had set perfectly firm. 
The culture chamber was a bell-jar inverted over blotting-paper on a glass 
plate. The whole was washed with a o.1 per cent. solution of corrosive sub- 
limate, and the blotting-paper was saturated with it. The plates to be ex- 
amined were placed in the chamber, and after four days the points of growth 
were counted. hyiers 
The result showed 200 centres of growth from one cubic centimetre of the 
water, of which about one-fourth liquified the gelatin. The number of germs 
is not excessive, and there was nothing whatever to justify the condemnation 
of the ice. 
(To be continued.) 
——— 
Enamel and Dentine. Some thoughts on the new theory concerning 
their structure.* 
By GEORGE S. ALLEN, 
NEW YORK CITY! 
During the last eight or nine years articles from the pens of either Drs. Ab- 
bott, Bédecker, or Heitzmann have upheld the idea that these are living tis- 
sues, and that a living protoplasmic reticulum had been demonstrated con- 
tinuous between the dentine and enamel and reaching into the protoplasm of 
the pulp cells. 
Such views are novel and not to be accepted suddenly on dogmatic asser- 
tion, or without good and convincing reasons. Accordingly the new views 
provoked much criticism and study of proofs offered and repetition of experi- 
ments. We present here a brief review of the results. First, no other 
workers have been able to corroborate the statements of the original authors 
of the theory, notwithstanding the fact that the technical methods present no 
great obstacles. It is a weakness of their work that they used gold chloride 
or osmic acid, neither of which exhibit any special affinity for protoplasm. 
Again, a protoplasmic reticulum must be of a soft, semi-fluid character, 
and could not exist in a dessicated tooth, and the process of preparation must 
destroy it even if present. Chemical analysis, too, ought to reveal the pres- 
ence of as considerable an amount of animal matter more than is given for 
enamel. But reasoning should not do away with demonstrated fact, and the 
writers, in their beautiful plates, show a reticulum in all its details. The 
original sections were, however, examined and afforded most convincing 
proof of the non-existence of the reticulum. In a letter from Dr. R. R. 
Andrews, of Boston, who examined the section on which Dr. Abbott had 
based published statements, he says: ‘In regard to the new theory of the 
structure of enamel, I have examined many slides of this enamel, some of 
which were examined by Prof. Heitzmann in his laboratory and pronounced 
by him to show the reticulum.’ ‘ These specimens I have examined critically 
with a most excellent ;!; objective of Tolles, and am assured that nothing like 
the reticulum figured by him can be demonstrated inthem. In regard to the 
recent study of Prof. Abbott’s slides, which he so kindly loaned me for that 
purpose, I could find no appearance whatever of fibrils resembling the exqui- 
site drawings made by Prof. Heitzmann, illustrating the article published in 
a 
* Abridged from Dental Cosmos, June, 1887 
