8 
bird, but probably quite as much, and in the opinion of many farmers even 
more, depends upon the nutritive conditions of the bird. Fig. 2 and its 
explanation shows how nutrition acts in influencing the feathergrowth. 
When a bird is in excellent condition from high feeding on lucerne or rape 
a more copious supply of blood circulates in the pith of the feather, more 
of the blood plasma exudes through the walls of the blood-vessels and bathes 
the feather-forming cells; this stimulates them to increased growth and 
multiplication, which means greater length and strength in all the parts 
concerned. The barbule-forming cells being furthest from the pith share 
in this increased nutrition to a greater proportionate degree than the barb- 
forming cells, hence we get an increased growth in the length of the barbule 
and the greatly desired density to the feather. 
Whatever be the strain of the bird, a high-class plume is not produced 
unless the nutritive conditions are also favourable. The ostrich is exceed- 
ingly sensitive in this respect as regards its feathers, and probably most 
farmers have been disappointed at times in not getting from superior birds 
the superior clipping they were known to have produced in the district 
from which they were purchased. Do what he will and provide himself 
with the best strains possible, a farmer will not produce the best result 
unless the nutritive conditions for his birds are highly favourable, and know- 
ing the nature of the parts of the feather we can now more readily under- 
stand how this comes about. 
