356 TlMEHRI. 
effect additional to, and distinct from, the modification 
of their colour, has been heard of by me only in this 
case. Secondly, we have evidently to do here with a 
belief referable to the old ' doctrine of signatures,' 
the doctrine that taught that certain external marks 
evident on any object, plant, animal, or other, indi- 
cated the possession of certain internal charatters 
by that object. A well-known illustrative case of 
this doctrine is that of the pretty little English field - 
flower called eye-bright [Euphrasia), which 'is sup- 
posed to be good for the eyes, on the strength of a 
black pupil-like spot in its corolla.' In our present case, 
the ' signature ' on the frog is its bright colour, which is 
evidently regarded as the outward and visible sign of 
certain internal qualities ; so that a little of the blood of 
the frog inserted, by a sort of process of inoculation, in 
the body of a bird will, it is supposed, produce the same 
external sign, that is brilliancy of colour, in the -new 
feathers of the latter. This doctrine of signatures is im- 
portant to our present purpose as it probably explains, 
as will presently be shown, many, though not all, of the 
facts observed in the artificial production of colour in 
feathers. 
2. The next instance to be mentioned is one to which 
I have already alluded in an earlier volume* of Timehri, 
where is told that I myself found the Macoosis, here in 
British Guiana, in the common possession of birds with 
altered plumage, and that the owners asserted that they 
produced this effect, caused yellow feathers to grow, in 
place of red, green, or blue, on parrots and macaws, by 
plucking out the natural feathers, rubbing the part of 
* Timehri Vol. I. p. 28. 
