GENERAL COXSIDERATIOX OF DISEASE. 39 



in the causation of disease. The very young animal is struc- 

 turally more delicate than the matured animal. Tissues are more 

 or less permeable to the various bacteria, and until the youn^;; 

 acquire an immunity, i. e., establish a resistance, thev are more 

 or less influenced by bacterial activity in their tissues. There 

 are some diseases, however, that affect onh ynuu','- animals, as, 

 canine and colt distemper, wdiile Lather diseases occur primarih' 

 or only in adults as carcinomata and bursattae. 



Sc.r is of consequence in the occurrence of disease. Parturi- 

 tion predisposes females to disease. Males arc especialU- suscept- 

 ible to urethral calculi. 



Genus may be a characteristic factor in the predisposition to 

 disease. Glanders is a disease of the genus equus, caseous-hinph- 

 adenitis of the genus ovis, canine distemper of the genus canis, 

 rinderpest of the genus bovis. 



Breed. — ^There are certai.n peculiarities of dift'erent breeds of 

 animals that are induci\-e to disease, thus the original Ch'desdale 

 horse is not resistant to laminitis ; the thoroughbred having a 

 nervous temperament is more susceptible to heart disturbances: 

 the jersev cow with a diminished breathing capacity is more 

 liable to pulmonary tuberculosis. 



White or light colored aniiimls are more susceptible to der- 

 matitis and are more affected by flies than those of darker color. 

 In certain locations there are no white hogs because the hogs 

 in those locations feed upon the roots of Lacuanthis tinctoria. 

 which causes a pink discoloration, (hyperemia), of their bones 

 and causes sloughing of the feet in all except black hogs. 



Ti'dvi'idiials of a resistant strain arc sometimes especially sus- 

 ceptible to certain diseases. 



Location. — The soil of a locality may be deficient in some 

 necessar^' ingredient or contain some no.xious constituent. Some 

 localities may be continually damp and muddy, others dry and 

 dusty, and still others abound in objectionable gases and odors. 

 Anv of the above conditions naturally diminish the resistance of 

 animals ; thus pica exists in localities in which the soil is prob- 

 ably deficient in some ingredient, scratches and thrush are com- 

 mon where mud abounds : broken and cracked feet in dry dusty 

 regions, and nasal catarrh where irritating odors are common. 



Climate definitely influences the hairy covering of animals. 

 In Angora, not onlv goats but also collie dogs and cats have 

 fine fleecy hair. Mule.s kept in mines constantly for a long time 

 become covered with velvety hair like that of a mole. 



Season.—Some diseases are more common in certain seasons. 



