BUREAU OF ANIMAL INDUSTEY. 



129 



Sources of infection and ways in which hog cholera may reach the herd, 16 



counties, IQl-i. 



Supposed source of infection. 



Herds. 



Per cent. 



From near-by sources: 



Exchanging labor and visiting Infected premises. 



Exposure of sick hogs on adjoining farms 



Harbored infection 



Dogs 



Per cent from near-by sources . 



From distant sources: 



Infected cars and public highways . 



Purchase of new stock 



Contaminated streams 



Birds 



Per cent from distant sources. 

 Indefinite 



Total. 



645 

 235 

 463 

 267 



33 



95 



45 



482 



526 



2,791 



23.10 

 8.42 



16.59 

 9.57 



57.69 



1.18 



3.40 



1.61 



17.27 



23.46 



18.85 



Experimental work has shown that hogs treated by the serum 

 alone may remain immune from three weeks to three months, and 

 that the simultaneous method produces an immunity which appears 

 to last in most cases for life. The following table gives the results 

 of observations made in all of the 16 counties in which the work was 

 conducted in 1914. In several of these counties the work did not 

 begin until midsummer, and in some of them not until September 

 and October, so that in some cases the lapse of time has not been 

 sufficient for the immunity to run out : 



Recrudescence of hog cholera in treated herds, 16 counties, 191 Ji. 



The next table gives the results in the three counties in which work 

 was begun in 1913, and in which the observations have extended over 

 the entire year 1914: 



Recrudescence of hog cholera in treated herds, three counties, lUl^. 



1 These herds were treated between Nov. 1 and Jan. 1, therefore in most cases sufficient time for reinfection 

 had not elapsed when this summary was prepared. 



22814°— AGB 1915 9 



