PREVENTION AND TREATMENT OF DISEASE 339 



fattening, but dangerous if too long continued. Poisons also are in 

 this class of causes of diseases. 



Enviromental causes of disease. Errors in locating poultry houses 

 and yards, faults in construction and regulation of poultry houses, 

 unsanitary conditions in houses and yards, errors in incubation and 

 brooding, disturbances affecting comfort and regularity of life (such 

 as rough treatment by attendants and fright by passing persons or 

 animals), are the common environmental causes of disease in poultry. 



Contagious diseases. Epidemics, as a rule, make little trouble 

 among healthy flocks kept under good sanitary conditions. Some 

 of the most virulent (as cholera, fowl typhoid, and bacterial enter- 

 itis) sometimes seem to be equally dangerous to all kinds of stock 

 under all conditions, but in view of the general absence of con- 

 tagious diseases from plants where conditions are good, and of 

 the efficacy of proper attention to hygiene and sanitation in stamp- 

 ing out contagion, it may well be doubted whether even the germs 

 of such contagious diseases are dangerous to poultry that are sound 

 in constitution and living in proper surroundings. When epidemics 

 of roup and enteritis break out, they are usually attributed to con- 

 tagion, but contagion seems to be effective only when other causes 

 prepare the way for it. Scaly leg and various skin diseases are 

 plainly transmitted in some cases, yet in nearly all affected flocks 

 some individuals are immune. 



Symptoms of disease. Indications of disease are general (com- 

 mon to many diseases) and special (peculiar to certain diseases). 



General symptoms of disease are of much more importance to 

 the poultry keeper than are special symptoms, except in cases where 

 the special symptom appears at first or at any early stage and is 

 plainly marked, as in skin diseas.es and in some throat and lung 

 troubles. General symptoms are negative rather than positive, in- 

 dicating lack of health, or of perfect health, rather than the pres- 

 ence of any specific disease. As control of disease depends largely 

 upon detecting it in the first stages and promptly using corrective 

 measures, it is of much more importance that the poultry keeper 

 should have a keen appreciation of the signs of health, and be 

 quick to observe any failing in them, than that he should know 

 the pronounced symptoms of diseases, for in a large proportion of 

 cases a disease cannot be identified by symptoms until it is so far 



