124 ANNUAL REPOKTS OF DEPARTMENT OF AGRICULTUEE. 



Tlie Chicago laboratory also collected and examined a number of 

 samples of water from various meat-packing establishments, made a 

 report upon the existence of the avian type of tuberculosis in swine, 

 and conducted some experiments with reference to the transmissibil- 

 ity of so-called hyperplasia of the bone marrow in cattle. 



The Omaha laboratory received and examined 308 specimens repre- 

 senting the usual variety of routine diagnoses. Examinations for 

 tuberculosis and hemorrhagic septicemia have increased, the former 

 due to cases of slaughter following reaction to the tuberculin test. 

 The similarity of lesions found in cases of certain affections of swine 

 to lesions of hog cholera made diagnosis sometimes difficult. 



Investigations pertaining to abortion disease have been made by 

 the branch laboratory at Ithaca, N. Y. 



BIOCHEMIC DIVISION. 



The work of the Biochemic Division, under Dr. M. Dorset, chief, 

 comprised chiefly, as before, investigations concerning hog cholera, 

 laboratory research Avork relative to meat products, studies of dips 

 and disinfectants, and the preparation of tuberculin and mallein. 



HOG-CHOLERA INVESTIGATIONS. 



The investigative work on hog cholera has been continued under 

 three general heads : (1) Methods of producing immunity, (2) modes 

 of spread of the disease, and (3) the causes of hog cholera and related 

 diseases. 



METHODS OF PRODUCING IMMUNITY AGAINST HOG CHOLERA. 



Some additional work has been done with methods for refining old 

 hog-cholera serum (defibrinated blood). The method referred to in 

 last year's report, consisting in the addition to old serum of strong 

 solutions of sodium chlorid, folloAved by heat with aeration, has been 

 used further and found apparently satisfactory. It has been found 

 also that the use of strong solutions of sodium chlorid may be dis- 

 pensed with wdien the serum is diluted with several volumes of 1 per 

 cent salt solution, containing a sufficient amount of phenol to produce 

 a concentration of one-half of 1 per cent in the final mixture. This 

 diluted serum is heated and aerated as in the other method. It has 

 been found possible by this process, which includes filtration and 

 precipitation of the globulins and antibodies, to refine and concen- 

 trate old defibrinated-blood antitoxin. 



A further study of the effect of phenol (0.5 per cent) on the 

 tuberculosis bacillus has indicated that the phenol alone can not 

 be depended upon to destroy that organism in clear serum or in 

 defibrinated blood, though it appears, after prolonged contact, 

 either to attenuate the bacilli or to reduce the numbers veiy ma- 

 terially. 



As a means of overcoming difficulty experienced by commercial 

 firms in effectively maintaining proper temperatures in heating 

 serum, the division has devised a method which makes it possible to 

 heat serum at a definite temperature for any desired period of time 

 without the use of the thermoregulator customarily employed. This 

 is accomplished by the use of a double- jacketed kettle, the outer 



