BUREAU OF ANIMAL. INDUSTRY. 151 



Previous tests showed that one five-thousandth of a cubic centi- 

 meter of blood from a pi^ sufferings from hog cholera was sufficient 

 to induce disease in a susceptible pig when administered subcutane- 

 ously. Further studies of this question of the minimum lethal dose 

 of hog-cholera virus have shown that the disease may be produced 

 by as little as one twenty-five-thousandth of a cubic centimeter. Fur- 

 ther. studies along this line are being carried out. 



Occasion was had to test again the potency of clear anti-hog-cholera 

 serum prepared in 1917. The serum, 4 years old, was found appar- 

 ently to be as potent as when it Avas prepared. 



Virus was furnished to a number of commercial plants upon re- 

 quest, to enable them to renew strains of virus which they were 

 employing in the production of hog-cholera serum. 



A study of the period of incubation of hog cholera was made pri- 

 marily with the object of obtaining data which might be helpful to 

 serum producers in selecting virus used in the production of anti-hog- 

 cholera serum and in selecting virus used with the serum for simul- 

 taneous immunization. The results showed that followinp- the sub- 

 cutaneous injection of blood 'from a pig sick of hog cholera about 50 

 per cent of the sui^ceptible pigs showed visible symptoms of disease 

 on the fourth day : that b}' the end of the fifth day more than 81 per 

 cent showed symptoms of disease, and by the end of the sixth day 

 more than 98 per cent exhibited visible symptoms. These observa- 

 tions led to the conclusion that hog-cholera virus which will produce 

 visible symptoms and a rise in temperature in 50 per cent or more 

 of susceptible pigs on the fourth day after subcutaneous injection, 

 and which has the power to cause progressive disease so that a con- 

 siderable majority of the injected pigs are "off feed" on the fifth 

 day, will produce a good serum, will be adequate for making serum 

 tests, and will result in a lasting immunity when properly admin- 

 istered with anti-hog-cholera serum. 



A study of various strains of Bacillus suifesHfev isolated at dif- 

 ferent times from different sources has developed the interesting 

 fact that there appear to be two groups of this microorganism. One 

 of these produced blackening of lead acetate agar while the other did 

 not produce blackening. These characteristics seem to be fixed. A 

 preliminary study of the agglutination reactions led to the belief 

 that the two strains are not serologically identical. A, paper re- 

 porting this and further work and its application with regard to cul- 

 ture media has been submitted for publication. 



The chemical studies of anti-hog-cholera serum and the effect of 

 preservatives on the proteins of hog-blood serum have been continued. 

 Two new methods for the determination of globulins in serums have 

 been worked out and published during the year. Further study is 

 being given to the chloroform-hemoglobin reaction, which is used as 

 described in the last annual report for the concentration and refining 

 of old defibrinated blood serum. A study of the effect of formalde- 

 hyde on serum proteins has been nearly completed. It has been 

 noted that there are certain differences in hogs' blood with respect 

 to the reaction to formaldehyde. Some of the blood serum gelatin- 

 ized in the presence of suitable amounts of formaldehyde, whereas 

 other serums did not undergo this change under the same conditions. 



25684— AGR 1923 11 



