338 POULTRY CULTURE 



from the observation of symptoms to the investigation of condi- 

 tions, examine systematically into matters of hygiene and sanita- 

 tion, mark every wrong condition as a possible cause of trouble, 

 and correct that condition, whether the trouble can be directly 

 connected with it or not. 



Causes of disease. The causes of disease are (i) constitutional 

 (arising from defects of the organism) ; (2) dietetic (caused by 

 improper food and feeding) ; (3) environmental (due to improper 

 surroundings) ; (4) contagious (communicated by contact). It is not 

 necessary to discuss these exhaustively. Only a few of the more 

 important of each class need be mentioned. Causes of disease are 

 not always clearly referable to one of these classes. A single cause 

 acting independently rarely produces disease, but it may open the 

 way for the operation of other causes. In such a case it may not 

 be clear which is the primary cause, but that point is immaterial. 



Constitutional causes of disease. Defects of the organism are 

 of two kinds : congenital (or inherited) and functional (or spon- 

 taneous). A creature may have a constitution generally weak or 

 defective in some respect because one or more of its ancestors 

 had. As a rule, it will not have a sound constitution unless its 

 immediate parents have sound constitutions. No matter how good 

 the constitution may have been originally, it may be impaired, either 

 at some point or as a whole, by accident, or by overworking an 

 organ, or through any external disease-producing cause, and never 

 regain its full tone though the conditions which caused the trouble 

 are removed and a decided improvement follows. In such cases 

 the functional weakness continues as a latent condition favorable 

 to the operation of the causes of disease. The most prevalent 

 constitutional cause of disease is debility, or low vitality, increasing 

 from generation to generation in stocks kept under highly arti- 

 ficial conditions. 



Dietetic causes of disease. Poor quality of food, ill-balanced 

 rations, overfeeding, underfeeding, and irregular feeding are the 

 principal dietetic causes of disease. As was shown in discussing 

 the relations of methods of feeding to other factors in the manage- 

 ment of poultry, the same ration may be, under some conditions, 

 good, under others, bad ; suitable for one bird, not suitable for an- 

 other ; useful for a special purpose or up to a certain point, as in 



