46a EXPERIMENT STATION. [Jan. 



Hog Cholera Ixvestigatioxs. 



The department continues to carry on its experiments with a 

 herd of garbage-fed hogs kept in co-operation with a farmer in 

 Amherst. The number of animals varies at different seasons of 

 the year from 75 to 150, All old and young pigs are given the 

 "simultaneous" treatment, consisting of an injection of anti- 

 hog cholera serum and virus administered at the same time. 

 Each successive crop of 5'oung pigs, spring and fall farrowings, 

 has during the past two or three years been given the "single" 

 treatment at about the age of eight weeks, this treatment con- 

 sisting of the administration of about 20 cubic centimeters of 

 anti-hog cholera serum without the virus. The immunity pro- 

 duced by this injection of serum continues until the animal 

 attains a weight of about 50 pounds, when it is given the 

 double or "simultaneous" treatment that ordinarily protects 

 against hog cholera infection for the remainder of the life of 

 the individual. One of the objects of study is to determine 

 whether or not it is possible to develop a strain of hogs pos- 

 sessing sufficient inherited immunity so that the trouble and 

 expense of the single treatment that is given at the weaning 

 age may, with safety, be omitted. Other problems under in- 

 vestigation refer to the kind and amount of serum and virus 

 required to produce a lasting immunity, the relation between 

 hsemorrhagic septicpemia, necrotic enteritis, suppurative pneu- 

 monia, hog cholera, etc. 



During the past year there has been some difficulty experi- 

 enced in procuring the materials necessary for the conduct of 

 the experiments connected with hog cholera. 



Incomplete Studies. 

 AVhen Dr. Gage left the department in February, 1918, to 

 enlist in the army service he had three studies relative to 

 Bacterium imUorum under way. These were enumerated in the 

 last annual report, as follows: — 



1. Bacterium pullor^mi infection. 



2. A comparison of the antibodies of B. pulloriim with those of the 

 B. coli-B. typhi-B. dysenterm group of agglutinins. 



3. The toxicity of B. puUontm products. 



