10 HISTORY OF 



of the kidneys by their whiteness. This milky substance ihejf 

 have in greater plenty than the more thin and serous part ; and 

 it is of a middle consistence, between limpid urine and the gross- 

 er parts of the faeces. In passing through the ureters it re- 

 sembles milk curdled or lightly condensed : and being cast forth, 

 easily congeals into a chalky crust." 



From this simple conformation of the animal, it should seem 

 that birds are subject to few diseases ; and in fact, they have 

 but few. There is one, however, which they are subject to, 

 from which quadrupeds are, in a great measure, exempt ; this is 

 the annual moulting v.hich they suffer ; for all birds whatsoever 

 obtain a new covering of feathers once a year, and cast the old. 

 During the moulting season, they ever appear disordered ; those 

 most remarkable for their courage, then lose all their fierceness ; 

 and such as are of a weakly constitution, often expire under 

 this natural operation. No feeding can maintain their strength ; 

 they all cease to breed at this season ; that nourishment which 

 goes to the production of the young is wholly absorbed by the 

 demand required for supplying the nascent plumage. 



This moulting time, however, may be artificially accelerated , 

 and those who have the management of singing birds frequently 

 put their secret in practice. They enclose the bird in a dark 

 Mige, where they keep it excessively warm, and throw the poor 

 little animal into an artificial fever ; this produces the moult ; 

 his old feathers fall before their time, and a new set take place, 

 more brilliant and beautiful than the former. They add, that it 

 mends the bird's singing, and increases its vivacity ; but it must 

 not be concealed, that scarcely one bird in three survives the 

 operation. 



The manner in which natui-e performs this operation of 

 moulting is thus : the quill, or feather, when first protruded 

 from the skin, and come to its full size, grows harder as it grows 

 older, and receives a kind of periosteum or skin round the shaft, 

 by which it seems attached to the animal. In proportion as the 

 quill grows older, its sides, or the bony part, thicken ; but 

 its whole diameter shrinks and decreases. Thus, by the thick- 

 ening of its sides, all nourishment from the body becomes more 

 sparing ; and, by the decrease of its diameter, it- becomes more 

 loosely fixed in its socket, till at length it falls out. In the 

 meantime the rudiments ot an incipient quill are beginning be- 



