THE ADIPOSE LOBE OP THE PELVIC PIN OP THE SALMON. 717 
compouud in virtue of the cbroixiiutn oxide which it contains 
is able to form a lake with hgematoxylin. It is necessary, 
however, to distinguish two kinds of fat. The fats in which 
no unsaturated grouping occurs are not acted on by the 
biclu’omate solution. On the other hand, where the molecule 
of fat contains such a group there occurs a slow pi’ocess of 
oxidation, and it is while this oxidation is going on that the 
insoluble fat-chrome compound is formed. The blue sub- 
stance which then results from staining is a threefold body 
con:posed of fat, mordant, and dye. It becomes clear, there- 
fore, that only the unsaturated fats can be stained by this 
process, and that on account of the ease with which they can 
be oxidised by the bichromate. We found also that the 
method may be applied to the staining of lipoid bodies in 
which unsaturated groupings occur such as cholesterin and 
cerebrosides. 
“In the next place it is interesting to find that as the 
bichromating goes on and the fat becomes fully oxidised and 
saturated a stage is reached at which no staining takes place. 
It is only during the process of oxidation that the chromium 
oxide combines with the unsaturated molecule in such a way 
that it can lake the haeinato.xylin. Olein, for example, when 
oxidised by bichromate of potassium yields finally dioxystearic 
acid, and this fat will not stain by these methods.^’ 
A number of sections of the adipose lobe 5 mm. thick, from 
a ripe female fish taken in ihe Wye nets, were prepared on the 
freezing microtome. 'I'hese were then placed in a saturated 
solution of potassium bichromate and kept at a temperature 
of 86° C. In order to observe the effect of oxidation induced 
by this treatment, sections were removed at intervals of 
twenty-four hours, and subjected to the haematoxylin (Kult- 
schitzky) test as described above. For two days no colora- 
tion took place; on the third day two minute blue specks 
wei'e observed, showing that oxidation had begun, and on 
each of the succeeding days up till the eighth very few blue 
specks appeared. On the ninth day the first obvious blue 
coloration was noted ; the next day the specks were fewer, 
