DISEASES OF POULTRY. 29 



tity of water, and the skin has no sweat glands, so that 

 but an insignificant amount of moisture is evaporated 

 from the external surface of the body. The lungs and 

 air sacs of birds must, therefore, perform not only the 

 duties which devolve upon the respiratory organs of 

 mammals, but also largely those of the kidneys and 

 skin as well. 



On the whole, the bird's respiratory apparatus is 

 very perfect and more active than that of any mam- 

 mal. The quantity of carbonic acid exhaled is very 

 large, the breathing is rapid, and the oxidation of the 

 blood is necessarily thorough to maintain the high 

 temperature of the bird's body. With all of this, birds 

 are capable of great and prolonged muscular exertion ; 

 the " wind " of the Homing Pigeon, for instance, being 

 something remarkable. 



The intimate connection which exists between the 

 bronchi and air sacs readily permits of the extension of 

 a disease process from one to the other, and parasites 

 or parasitic diseases may be common to both. Injured 

 birds may even breathe through a broken humerus 

 which has pierced the skin, when their windpipes are 

 obstructed with blood and impermeable to air. In this 

 case the air is drawn into the lungs through the inter- 

 clavicular air sac instead of penetrating by way of the 

 trachea and bronchi. The respiratory apparatus of 

 birds differs, therefore, to a remarkable extent from 

 that of other animals, in structure, in function, and in 

 the development and extension of the diseases to which 

 it is subject. 



SIMPLE CATARRH. 



One of the most common diseases of birds is catarrh. 

 It is sometimes mild, attacks but a few birds in a flock 

 and is easily overcome. At other times it is more 



