162 CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 



there is the same initial change — proliferation of the connective tissue. 

 The variations in the nature of the lesions depend on the different ac- 

 tivity of the intercellular substance and the connective tissue and endo- 

 thelial cells, on the disaggregation of the elements and the occurrence 

 of ulceration. Thus the fibrous growth is usually greatest where con- 

 nective tissue is most abundant, as in bones, cartilages, and interlobular 

 lung tissues, while the more cellular and rapidly disintegrating growth 

 occurs in connection with epithelial structures, as in the air cells and on 

 the inner coat of blood-vessels. This tendency to attack the connective 

 tissue and lymphatics, and to show products varying according to the 

 nature of the surrounding structures is common to other infectious dis- 

 eases, and notably glanders, chronic lung plague, actinomykosis, &c. As 

 in these cases, too, the morbid process is first localised and only becomes 

 diffused when it has attained a certain local intensity. Again, it agrees 

 with other infectious diseases in being favored by certain unhygienic 

 conditions, as damp pastures, close filthy buildings, overcrowding, poor 

 food, excessive work or milking, &c., yet is not absolutely dependent 

 on any one or more of these, nor due to these alone. As in these other 

 affections there is the disease germ — bacillus tuberculosis — the presence 

 of which is essential to the development of the disease, and its recogni- 

 tion completes the diagnosis. 



Again, there is a special constitutional predisposition in animals hav- 

 ing an excess of connective tissue and of lymphatic development as in 

 cattle and swine. 



Climate seems to have much effect, as the disease is virtually un- 

 known in northern and arctic climates — Iceland, Northern Norway, and 

 Sweden, Finland and Lapland — and very common in the temperate 

 and tropical regions. 



(While frost doubtless chains up this germ when out of the body, as 

 it does others, it must not be forgotten that the paucity of cattle in the 

 extreme north will even more tend to retard the propagation of this 

 disease. Other countries formerly free from tuberculosis have now, 

 by the influx of consumptive patients, and, in some instances, by the 

 greater density of the population, become extensively affected with this 

 disease, as witness the Hebrides, Australia, and our northwestern 

 States and Territories. — J. L.) 



To the same effect speaks the great prevalence of tuberculosis in 

 dairies near cities where the stock is often changed and new stock is 

 being constantly purchased, and its almost complete absence from dis- 

 tricts exclusively devoted to breeding and never importing strange 

 stock. This is but a repetition of what is known of other contagious 

 diseases. Wild races, too, living in the open air are largely exempt. 



Heredity as a cause of tuberculosis. — In favor of the heredity of tuber- 

 culosis Jj.vdtin quotes from over a score of veterinary authors. The 

 congenital presence of the disease is proved by quotations from Konig, 

 Stirnimann, Adam, Butscher, Virchow, Semmer, Jessen, Fischer, Miil- 



