12 E VOL UTION AND DISEASE. 



types among normal cutaneous horns, not only in birds 

 but among mammals, as parallels to the annual shedding 

 of the pathological cutaneous horns of birds. 



Not infrequently tumours are found in certain abdo- 

 minal organs and in the subcutaneous tissues of man 

 and other mammals, possessing skin and its appendages 

 such as hair, wool, and glands. Such tumours contain 

 in man, horses, and oxen, hair ; in pigs, bristles ; in 

 sheep, wool ; and in birds, feathers ; thus harmonizing 

 with the physiological characters special to the animal in 

 which such tumours occur. Further, the hair in such 

 tumour becomes grey as age advances, and like that on 

 the exterior of the body is shed, so that such tumours 

 may in the long run become literally bald. 



Without attempting to multiply instances, such facts 

 as these were sufficient to induce me to pursue the 

 inquiry into Zoological Pathology, or General Pathology 

 in the fullest sense, and the latest views and investiga- 

 tions in this wide, but little cultivated, field are sum- 

 marized in the ensuing pages. 



Wherever possible, physiological types of diseased 

 (pathological) processes are described ; the illustrations, 

 whenever practicable, have been selected from animals 

 other than man, for in him they have been too exclusively 

 studied ; indeed, by restricting our inquiries to man it 

 is impossible to frame any generalizations concerning 

 disease upon a sound basis. It has been stated that " a 

 knowledge of human anatomy is sufficient for the mere 

 art of the surgeon." This may be correct, but it is quite 

 certain that if we restrict our observation of the processes 

 of disease as they occur in man, our notion of them 



