EXPERIMENTS WITH OSTRICHES— X. 
HOW THE BARS IN OSTRICH FEATHERS ARE PRODUCED. 
By Professor J. E. Duprpsn, M.Se., Ph.D., A.R.C.8., Rhodes Univer- 
sity College, Grahamstown. 
The experiments in connection with the investigations of the bars in 
ostrich feathers have progressed so far that a definite understanding has 
been. reached as to how the defects are produced; on the other hand the 
endeavours to work out a remedy for their prevention have made con- 
siderable progress, but are not yet concluded. The following account of 
how the bars are formed wili assist in an understanding of some of the 
difficulties involved in their prevention, and may direct attention towards 
a solution. 
It is suggested, for reasons which will be evident later, that the name 
shrinkage bar should be applied to the ordinary kind of bar with which 
all ostrich farmers are familiar. | It will serve to distinguish it from 
others known as poverty bars, constriction bars, and vertical bars, the for- 
mation of which will be described on another occasion. 
Shrinkage bars are by far the most familiar and the most important 
of all the structural defects of the ostrich feather. It is rarely, if ever, 
that the plumage of a bird is altogether free from them, and when pre 
sent in any number they lead to a serious depreciation in the value of the 
plumes, since they represent so many faults and weaknesses in the con- 
tinuity of the flue. They are found on ostriches of all ages, though per- 
haps more frequently in chicks and young birds; moreover, they occur on 
the plumes of the wild ostrich as well as on those of the domesticated bird, 
and similar imperfections are occasionally to be seen on the feathers of all 
other kinds of birds. ) 
Such a wide distribution as the above indicates that the barring de 
fects are to be associated with something fundamental in the formation of 
feathers generally, not anything peculiar to the ostrich. It will be shown 
that their immediate formation, at any rate in the ostrich, is due to the 
shrinkage of the plastic feather-sheath around the soft and growing parts 
of the feather; and also that the shrinkage invariably takes place at cer- 
tain well-defined places, which represent the weaker growth at night, re- 
sulting from a diminished physiological vigour. Produced in this way 
they may reasonably be expected to occur in all birds, since the feathers 
of all are formed alike. 
The appearance of a shrinkage bar is but too familiar to anyone in- 
terested in ostriches or ostrich plumes (Fig. 1). It consists of a break or 
fault in the regular formation of the flue, a narrow interruption extend- 
ing in an oblique manner across the feather, but not often passing all the 
way along both sides; the outer side of the shaft also may be notched at 
the same level. Looked at carefully a single bar is seen to represent a 
defect at practically the same place on each barb, and the actual defect 
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