ON HYDROCYANIC ACID. 
313 
the front wall of the permanent tooth, in a perpendicular direction, 
from its top or face to the gum, which is entirely absent in the 
temporary one, so that they are readily distinguished either in the 
jaw or out of it. The molar teeth arise from their respective alve- 
oli by a thin marginal elevation of enamel, of an oblong quadri- 
lateral figure ; grooved, indented, and channelled, by three cavities 
on the face or crown. These cavities or pits fill up, or rather dis- 
appear, as the teeth increase in size, by growing solid from their 
base and the apices wearing away. The cavity on the inner side 
of the tooth disappears first, and the other two are effaced about 
the same time. 
I have here given a succinct sketch of the temporary and per- 
manent teeth for the purpose of shewing that there are some remark- 
able differences of character and particular changes and alterations 
of them taking place as the animal becomes aged ; and it is left 
for me to again repeat, that, to test the age by the horse’s teeth, the 
subject must be well studied from the mouth alone. First, the 
tooth is cut and gradually grows to a level with the adjacent one ; 
and, secondly, the crown wears away until the pit or mark is lost 
to view : therefore it must be quite obvious that a period is re- 
quired for each of these purposes, and that the wasting away of 
the mark will not commence until the tooth has attained its level 
with those on each side of it. Experience will teach that these 
interesting phenomena take place with a precision on which the 
constant observer will rest perfectly satisfied that the age is cor- 
rectly shewn by them to a much more limited period than twelve 
months, or even six. 
To conclude : — Mr. Goodwin, in his communication, says nothing 
about the molars in the mouth of the colt shewing for four years 
old. There is one remarkable phenomenon connected with them 
alone, viz. the third molar tooth has two pits or marks uneffaced 
at four years, while in the first, second, fourth, and fifth, they are 
quite obliterated. 
ON HYDROCYANIC ACID AS A POISONOUS 
AGENT. 
By W. A. Cherry, M.R.C.V.S. 
Hydrocyanic acid, one of the most certain destroyers of 
animal life, does not produce death in the horse so suddenly as it 
is popularly believed to do. I shall proceed to shew that such is 
the fact ; and though my opportunities for examination, as to the 
