ON COD-LIVER OIL. 
147 
It will be unnecessary to enter into any details with re- 
spect to the other constituents of the oil. 
The characters by which we judge of the genuineness, 
purity, and goodness of the oil are partly physical, partly 
chemical. 
The physical characters which are usually employed are 
principally colour, odour and flavour. The finest oil is that 
which is most devoid of colour, odour, and flavour. The 
oil is contained in the cells of the fresh liver, is nearly 
colourless, and the brownish colour possessed by the ordi- 
nary cod-oil used by curriers is due to colouring matters 
derived from the decomposing hepatic tissues and fluids, 
or from the action of air on the oil. Chemical analysis 
lends no support to the opinion, at one time entertained, 
that the brown oil was superior, as a therapeutical agent, 
to the pale oil. Chemistry has not discovered any substances 
in the brown oil which could confer on it superior activity 
as a medicine. On the other hand, the disgusting odour and 
flavour, and nauseating qualities of the brown oil, preclude 
its repeated use. Moreover, there is reason to suspect that, 
if patients could conquer their aversion to it, its free use, 
like that of other rancid and empyreumatic fats, would dis- 
turb the digestive functions, and be attended with injurious 
effects. 
Of the chemical characters which have been used to de- 
termine the genuineness of cod-liver oil, some have refer- 
ence to the iodine, others to the gaduin or to the bile con- 
stituents. I have already stated that some fraudulent 
persons are said to have admixed iodine (either free iodine 
or iodide of potassium) with train oil to imitate cod-liver 
oil. The presence of this substance may be readily detect- 
ed by adding a solution of starch and a few drops of sul- 
phuric acid, by which the blue iodide of starch is produced ; 
or the suspected oil may be shaken with alcohol, which ab- 
stracts the iodine. 
