756 
electrolyte results in salting out the colloid whereby the particles 
are at first so small that they are invisible to the unaided eye and 
that the fluid seems to be perfectly clear. Gradually the flakes 
become visible. But even in the phase in which they are still 
invisible, the extremely small particles are accessible to the ether 
and are dissolved in it. 
This interpretation also undoubtedly holds in the phenomenon 
observed by us with the lipochrome, when alkali or Al-sol, are 
added. However, it naturally does not account for the ‘‘liberating”’ 
action of some drops of alcohol, as in that case there is no question 
of precipitation. The alcohol, if added in adequate quantity, would 
rather change the colloidal solution into a true solution. 
We are unable to account for this phenomenon, but we believe 
it to be analogous to another reaction previously observed by us. 
In studying the bile-pigments we had detected that bilirubin, as found 
in bile and in the blood-serum of patients with obstructive icterus, 
is directly and completely capable of combining with diazonium salts. 
However, when the same reaction is performed in the blood-serum 
of patients suffering from what was formerly called hematogenous 
icterus, the reaction is retarded and incomplete. On addition of a 
small quantum of alcohol the reaction takes place directly and 
completely. 
We cannot but assume that the bilirubin in the serum in the 
case of obstructive icterus, and in the bile from the gall-bladder, is 
in a different condition from the bilirubin in the serum of patients 
with hematogenous icterus. In the latter case it would seem that 
the bilirubin particles cannot get in touch with the diazonium- 
solution, except through the action of small quanta of alcohol. This 
behaviour of bilirabin in the serum from hematogenous icterus is 
similar to that of lipochrome in cow’s serum. 
The resemblance in the behaviour of an aqueous colloidal solution 
of carotin to that of the native cow’s serum containing lipochrome, 
suggests the idea that, also in the sernm the carotin occurs in a 
colloidal and analogous condition. However, this seems not to be 
the case, since in the aqueous colloidal solution the lipochrome is 
precipitated by the above-named substances (NaOH, Al-sol, etc), so 
that it can be extracted with ether. On the other hand, when adding 
these reagents to the native serum, the pigment will not pass over 
to the ether. 
Another remarkable difference between the native serum, con- 
taining lipochrome and the artificial colloidal solution, is the action 
of light. Barlier researchers detected already that carotin from 
