RKTROGRESSIVE TISSUE CHAN(;ES. 249 



Some of the pigment is carried out bv leucocytes and some of it 

 is entangled in the cicatrix of the healing wound, where it re- 

 mains permanently. Tattooing is a very valuable means of 

 marking stock, as it gives a positive means of identiiication. 

 Registered cattle, horses, sheep, hogs, dogs, etc., are tattooed in 

 the ear, and fowls on the legs. The wound is made with an instru- 

 ment similar to a hog ringer, in which slugs containing needle 

 points arranged in the form of figures or letters are used. This 

 instrument is used to punch holes into the inner surface of the 

 external ear, immediately after which carbon is rubbed into the 

 wound. When the wounds are healed, the tattoo mav be easily 

 observed. 



Effects. — Excessive pigmentation of a tissue or tissues is of 

 little pathologic significance. Pigmented tissues are probablv 

 not hindered in their physiologic activities, excepting in so far 

 as the cause of the pigmentation is an etiologic factor in the dis- 

 turbance of the functioning of a part. Icteric jiigmentation is of 

 consecjuence because ijf the action of the bile upon nerve cells. 



rigmentation. especiallv when excessi\-c, is a basis for the 

 condemnation of meat and meat products because of public sen- 

 timent. 



ABSENCE OF, OR DIMINISHED PIGMENTATION. 



(Hypochr( miatosis. ) 



Visible pigmentation mav be less than normal, and in some 

 instances there is a complete absence of pigment. Areas con- 

 taining less pigment than normal and depigmented areas are 

 permanentlv white in color, as they are not aiTected with sun- 

 light or anv other conditions that tend to produce pigmentation. 

 This condition may be of antenatal or postnatal origin. 



Etiology. — Antenatal absence of, or diminished pigmentation' 

 may be inherited or it may be caused by disturbances of the 

 embryonic cells that produce normal pigmentation. Postnatal 

 absence of, or diminished pigmentation is usually the result of 

 disease in which areas of tissue have been destroyed and later 

 substituted by cicatricial tissue. 



The total absence of pigment (achromatosis) is not of com- 

 mon occurrence, being most frequent in rabbits, birds and rats 

 (albinos). An albino is an animal devoid of cutaneous and chor- 

 oid pigment, the condition being inherited or congenital. The 

 animals thus have white skin and usually white hair and their 

 eves are pink or red because of the absence of choroid pigment, 



