A total of 12 reindeer calves were divided into two groups and the vol
ume densities of liver cytoplasmic structures were counted using TEM.
The six animals in group 1 were allowed to graze freely while those in
group 2 were kept in pens and fed with lichens. All of them had a neg
ative energy balance and lost weight from November to April, group 1 b
y 14.9% and group 2 by 24.8%. In spite of the weight losses, no signif
icant changes in volume densities occurred during the winter. Glycogen
remained fairly steady and there was no fatty infiltration into the h
epatocytes. The very low incidence of Golgi apparatus in the hepatocyt
es may have been due to the inhibition of protein and lipid synthesis
during the winter. These results point to substantial adaptation to ex
treme environmental conditions. The animals in group 1 apparently move
d about more, which may have caused a greater breakdown of glycogen, r
esulting in turn in a lower volume density of glycogen in January and
March.