$3 
ture through the opaque spot with a curved needle, which 
serves to fix the eye. Another needle is then passed at 
right angles to the former, and armed with a very fine liga- 
ture, which is allowed to remain loose. The first liga- 
ture being then strained; an incision is made equal in 
length to the nebulous portion; then raising it by the ligature, 
the whole opaque portion may be removed with a sharp 
curved scissors, and by drawing the ligature of reserve, the 
two fresh incised surfaces brought together. 
Professor Kane read a paper “on the Composition of 
certain essential Oils.” 
The first object of the author, in commencing the exami- 
nation of this subject, was to collect facts towards an ap- 
proximate solution of the problem, ‘‘ whether there can be 
Sound any law connecting the composition of the secretions of 
plants of the same genus or natural family.” The three 
alcaloids of the genus cinchona, giving the formule 
R+0,R+20,R+30, 
appear to furnish a glaring instance of the existence of such 
a law; but the want of connexion in the composition of the 
constituents of opium might be advanced in opposition, 
although not quite a parallel case. The family of the 
coniferee appear well characterized by the presence of the 
hydrocarbon c,1, and its oxides; but the same composition 
is found prevailing among the aurantiz, as in oil of lemons, 
—the myrti, as in the neutral oil of cloves,—and the lauri, 
as in common camphor ; whilst other members of the same 
family, as oil of cinnamon, have formule altogether dif- 
ferent. 
The members of the family of the labiata are characte- 
rized by yielding remarkably aromatic oils by distillation ; 
and as many of these oils, from their use in medicine, are 
12 
