To injected tuberculous infection, quite independent of the character of the injection, guinea pigs have always been found to possess the high susceptibility with which they are commonly credited. This subject has been gone into at some length because it is of considerable importance in view of the extent to which guinea pigs are used by investigators in their studies of tuberculosis.

The examination of the feces of a number of tuberculous cattle showed that they are frequently very rich in acid-fast bacteria; that is, bacteria which have the microscopic appearance of and conduct themselves precisely like tubercle bacilli in the presence of various reagents. Such acid-fast bacteria could not be detected in the feces of the station cattle that are free from tuberculosis. In two cases, with the feces of two tuberculous cows, the acid-fast bacteria were definitely proved by inoculation tests to be tubercle bacilli. That the feces of tuberculous cattle may contain innumerable virulent tubercle bacilli must be regarded as a seriously important fact.

Cultures of tubercle bacilli which have been used since 1902 for the study of the transformation of characteristics of tubercle bacilli following their long-continued cultivation under artificial conditions have been kept under observation in the Pathological Division during the year, and the changes which have occurred in them have been noted.

Tubercle bacilli have been recovered from several rare animals at the National Zoological Park, such as the rattlesnake, the camel, the beaver, kangaroo rats, and the roughed or crab-eating fox, and it is of interest to note that these animals suffer from natural infections with tuberculosis, and that in most instances the micro-organisms present conform to the human type of tubercle bacilli.

DISTRIBUTION OF TUBERCULIN.

The demand for tuberculin, which is prepared in the Biochemic Division and furnished free of charge by the Bureau to authorized health officers in the various States and cities, greatly increased during the past year. The total amount of tuberculin prepared and shipped during the year was 103,510 doses, an increase of approximately 40 per cent over the amount sent out during the previous fiscal year.

HOG-CHOLERA INVESTIGATIONS.

In the previous annual report the results of the experiments con cerning the etiology of hog cholera were briefly described. The Biochemic Division, in pursuing this work further during the past fiscal year, has demonstrated that the filterable virus which has already been shown to be the primary cause of hog cholera in southwestern Iowa is also present in outbreaks of that disease occurring in eastern

Nebraska, in central Iowa, and in Virginia. The outbreaks which have been studied in these localities possessed all of the well-known characteristics of hog cholera. These experiments demonstrated that the filterable virus is not peculiar to hog cholera as it is found in southwestern Iowa, and they also indicated that this virus was widely distributed and probably the active causative agent of all outbreaks of that disease. A number of experiments having for their object the determination of the mode of transmission of the disease, the portal of entry of the virus into the hog's body, the length of life of the virus outside of the hog's body, and the nature of the virus itself have been carried out, and the results will all be published later in bulletin form.

In connection with the other experiments the bactericidal action of hog's blood has been investigated and the results are now ready for publication. It is very gratifying to note that these recent experiments have substantiated in every way the results published in Bulletin No. 72.

In addition to the work just described, a certain number of experiments concerning the production of immunity from hog cholera have been arrived at, these immunity experiments being based upon the recently demonstrated fact (see Bulletin No. 72, Bureau of Animal Industry) that the primary cause of hog cholera exists in the blood of hogs sick of that disease, but not in pure cultures of Bacillus cholerœ suis, which had previously been regarded as the cause of hog cholera. In a general way, the methods employed may be said to embrace the following general principles:

(1) The injection of hogs immune from hog cholera with blood from hogs sick of that disease.

(2) The drawing of blood from the immune hog hyperimmunized by injections of diseased blood, and the use of this immune blood, either alone or in conjunction with diseased blood, for immunizing healthy hogs or treating those sick of hog cholera.

By methods based on these principles we have secured from each of three different immunes, treated with different strains of diseased blood, sera which in doses of 10 c. c. to 20 c. c. afforded complete pretection to nonimmune hogs against an infection which was fatal to from 70 to 100 per cent of untreated animals.

In view of these favorable results the process was patented in such a manner as to insure to all the people in the United States the right to its use free of any royalty, the patent being taken out in this way by Dr. M. Dorset, chief of the Biochemic Division, who planned and directed the investigations. The number of experiments thus far carried out is not considered sufficient to warrant the present recommendation of this process for general use, but further experiments

are being pushed as rapidly as is consistent with thoroughness, and it is hoped that a detailed statement of the results obtained may be made during the present year.

Experiments in the prevention of hog cholera by selective breeding are being continued with the object of developing by artificial selection a race of hogs which will possess partial or complete immunity from hog cholera. This work, which is carried on by the Biochemic Division in cooperation with the Experiment Station, was begun several years ago, naturally immune hogs being used as a basis and each litter exposed to infection. Thus there were retained out of each litter only those animals which showed the greatest powers of resistance. Several generations of animals have been exposed to disease during the last two or three years and the work is still being carried on, but sufficient results have not been obtained to warrant an expression of opinion as to the final outcome.

GLANDERS.

During the year isolated outbreaks of glanders have been reported from various quarters, and material from suspected cases has been forwarded to the pathological laboratory for examination and diagnosis. Nasal secretions and tissues from horses were received from North Dakota, Connecticut, Maryland, Virginia, and the District of Columbia. The samples from Connecticut proved negative for glanders, but positive results were obtained from all other sources. Cases occurring in the District of Columbia come directly under the supervision of the Chief of the Bureau of Animal Industry, who directs the disposition of the animals, the isolation and testing of exposed animals, and the disinfection of the premises.

Of very great importance for the diagnosis of glanders is the Gruber-Widal reaction, first recommended by MacFadyean in 1896, which has been made use of during the past few years. It has been employed in a number of cases quite successfully, but up to the present time has not been used as a routine measure, as the character of most of the specimens received makes it necessary to rely for diagnosis either upon the Strauss inoculation method or the isolation of the specific bacillus itself. The Strauss method, in our hands, has also given excellent results, and but for the time required would be an ideal means of diagnosis.

The serum diagnosis (or the Gruber-Widal test) of glanders consists in the addition of fixed, definite quantities of blood serum from the suspected animals to young cultures of the Bacillus mallei, and, if the case be positive, results in an agglutination or aggregation of the isolated bacilli into small clumps, which eventually cling to the side or drop to the bottom of the tube of culture medium in which they have previously been held in suspension.

DISTRIBUTION OF MALLEIN.

The Bureau has continued to furnish mallein free of charge to authorized health officers and to the War Department, and during the fiscal year 10,105 doses, prepared by the Biochemic Division, were so distributed. This represents an increase of about 40 per cent over the distribution of the preceding fiscal year.

BLACKLEG.

The great demand for blackleg vaccine still continues, thus showing the confidence of the stock raiser in the efficacy of vaccinating his young cattle for the prevention of spontaneous outbreaks of this virulent disease. During the year there have been prepared in the Pathological Division and distributed among stock owners 1,350,915 doses of vaccine.

The results of inoculations for the year ending June 30, 1905, as reported to the Bureau by the stock raisers who have used the vaccine, are as follows:

Results obtained from vaccine distributed during the fiscal year ended June 30, 1905.

After eliminating the number of cattle which die within fortyeight hours after vaccination as a result of being already infected with blackleg at the time of injection, and those whose death has been due to mistakes in performing the operation, the number of cases that died after vaccination is reduced to 3,575, or 0.48 per cent, whereas the losses without the use of vaccine were formerly as high as 10 or 12 per cent of the calves produced annually in the infected districts.

RABIES.

Within the District of Columbia there has been a considerable reduction in the frequency of cases of rabies during the past year. Of the 30 suspected cases examined in the laboratory of the Pathological Division from all sources, 16 proved positive, of which number only 8 came from within the District, as compared with 13 for a similar period of time last year, or a reduction of 38 per cent. In the following table the source and species of the animals affected and the result of the experimental animal inoculations and microscopic examination of the plexiform ganglia, together with the number of persons or animals bitten, are given:

Results of inoculation tests and microscopic examination for rabies.

In the 10 positive cases in which the plexiform ganglia were sectioned there was only one case (No. 504) in which the lesions were not sufficiently marked to base a positive diagnosis without waiting two weeks for the rabbits to develop the symptoms, and in this case the dog was killed during the course of the disease. This demonstrates the necessity of allowing the animal to die naturally from the effects of rabies if an early diagnosis by means of a ganglia examination is to be assured.