DISKASKS OF POULTKV. 15 



lively, has a clear eye, a bright red comb, is quick and 

 active in its movements, has a good appetite and when 

 the various organs of the body perform their functions 

 in the manner in which they are observed to act in all 

 birds that are vigorous and thriving. On the other 

 hand, we say a bird is diseased when some function or 

 functions of its bod}' are not performed as thej^ are in 

 the great majority of indi\-iduals, or when some organ 

 presents an unusual form or appearance. Disease has, 

 therefore, been defined as a life the manifestations of 

 which deviate more or less from the normal. Practi- 

 cally, we say a bird is diseased when we observe that 

 one or more of its functions are not carried on in a 

 normal manner, or when we find unusual growths, in- 

 juries, or parasites affecting any of its organs. 



THE ORGANS AND APPAKATL'S AND THKIR FUNCTIONS. 



In the study of disease, one of the most important 

 things is to acquire the habit of looking at a bird, not 

 as one indivisible object, but as an individual made 

 up of many distinct parts, each of which has its special 

 function to perform. Thus, we find the beak, the 

 tongue, the oesophagus, the crop, the proventriculus, the 

 gizzard, the pancreas, the liver, and the intestines, each 

 separate and distinct in itself, and each liable to be 

 affected by disease. We observe also that these organs 

 taken together make up the digestive apparatus and 

 that they are associated together for the purpose of 

 obtaining, preparing, and assimilati.ig nutritive ma- 

 terial for the sustenance of the l)od3' as a whole. We 

 are often able to determine that there is something 

 wrong with the working of an apparatus before we are 

 able to locate the trouble in one or more organs. To 

 ascertain the seat of a di.sease and understand its nature, 



