ON COD-LIVER OIL. 
149 
colouration in fact depends on the action of the sulphuric 
acid on some one or more organic constituents of the oil, 
and the following facts lead me to infer that it is in part due 
to the presence in the oil of one of the constituents of the 
bile. 
It is well known that in 1844, Pettenkofer pointed out a 
new test for bile. If to a liquid supposed to contain bile, 
about two-thirds of its volume of oil of vitriol be added, the 
liquid kept cool, a few drops of a solution of cane-sugar 
(four or five parts of water to one of sugar) be added, and the 
mixture shaken up, a violet red colour is produced, provided 
bile be present. This test succeeds very well, if we dis- 
solve a little extract of ox-bile in water, and test the solu- 
tion with sugar and oil of vitriol. The colour developed 
agrees with that produced by the addition of oil of vitriol to 
cod-liver oil, which De Jongh has shown, contains the es- 
sential constitutents of the bile. 
Pettenkofer remarks, that the presence of a very great 
excess of chlorides will change the violet red-colour into a 
brownish-red. This fact is deserving of notice, because it 
may aid in accounting for the fact that some specimens of 
cod-liver oil strike a brownish-red, not a violet-red colour, 
with oil of vitriol. 
Strecker confirms Platner's observation that both cholic 
and para-cholic acids produce the same colour with sugar 
and oil of vitriol, as bile does; so that Pettenkofer's test 
doubtless acts on one or both of these acids. Now De 
Jongh has shown that cholic acid is contained in cod-liver 
oil, and we have, therefore good reason for believing that 
it is in part by the action of oil of vitriol on this acid, 
that the violet red colour is produced in cod-liver oil. 
But it is well known that for the development of this co- 
lour in bile it is necessary to use, besides oil of vitriol, a 
third agent (sugar.) Pettenkofer observes that for cane-su- 
gar we may substitute grape-sugar or starch ; in fact, any 
substance which can by the action of oil of vitriol be con- 
