TUBERCLE BACILLI IN MARKET MILK IN PHILADELPHIA."

By H. C. CAMPBELL, V. M. D., M. D.,

Expert in Milk Hygiene, Pathological Division.

INTRODUCTION.

That milk and its products may contain tubercle bacilli is a wellestablished fact. How tubercle bacilli may contaminate milk is no longer problematic, but has been definitely proven to occur in one of the following ways: Either before the milk is drawn from the udder, by direct passage of tubercle bacilli from lesions in the animal, or by contamination of the milk after it has been drawn from the udder by air, feces, or particles of foreign matter laden with tubercle bacilli.

It is generally accepted that there are several varieties of tubercle bacilli. As a rule, the one commonly found in milk is the bovine type, but the human type has been found in a few instances, which are regarded as examples or illustrations of the contamination of milk by a consumptive dairyman.

As milk is a universal food product, the question arises whether man can be infected with tubercle bacilli of the bovine variety. Different authorities hold different views upon this question. Many scientists are of the opinion that a large percentage of the cases of tuberculosis in children are of the bovine type.

Among the first to demonstrate that tubercle bacilli of a bovine type may be proven to be present in the lesions of children suffering from tuberculosis were Theobald Smith and Ravenel. Recent experiments conducted by the German commission, the British commission, and Fibiger and Jensen on tuberculosis show that in tuberculosis of children respectively 10 to 23 per cent of the cases are due to the tubercle

a The investigation reported in this paper was conducted in cooperation with the Pennsylvania State live-stock sanitary board.

Mohler, John R. Infectiveness of milk of cows which have reacted to the tuberculin test. U. S. Department of Agriculture, Bureau of Animal Industry, Bulletin 44.

Schroeder, E. C., and Cotton, W. E.

The danger from tubercle bacilli in the environment of tuberculous cattle. U. S. Department of Agriculture, Bureau of Animal Industry, Bulletin 99.

bacilli peculiar to cattle, thus locating the origin of 10 to 23 per cent of children's tuberculosis in milk. Park, of New York City, has recently confirmed these results, having found bovine tubercle bacilli in 26 per cent of the cases of tuberculosis in children under 5 years of age and 18 per cent of bovine tubercle bacilli in tuberculous children between 5 and 16 years old.

The percentage of tubercle bacilli found in the milk supply of large cities has been accurately determined in only a few instances. The results of eighteen to twenty investigations in European cities showed that 9 per cent of the milk samples contained active germs of tuberculosis. Anderson has shown that in Washington, D. C., approximately 11 per cent of the dairies supplied milk containing virulent tubercle bacilli. Hess has found 16 per cent of the milk supply of New York City to contain virulent tubercle bacilli.

METHOD OF COLLECTING THE SAMPLES.

It is difficult to determine accurately the presence of tubercle bacilli in the milk supply of a city, because of the fact that market milk may contain large numbers of other bacteria, and only a very small portion of any one sample can be used for animal inoculation, which seems to be the only trustworthy method of determining the presence of tubercle bacilli in milk. After noting the high percentages in other cities, it was thought desirable to make a careful study of the Philadelphia milk supply for the presence of tubercle bacilli. This work was begun on January 7, 1909, in the following manner:

The samples were collected in a systematic manner so as to cover approximately the entire city. The collecting of the samples as well as the other work was done by the writer, so as to avoid any danger of outside contamination. In collecting the samples pint glass bottles were used which had been previously washed, plugged with cotton, and sterilized. The various milk stores were visited and a sample as sold over the counter to the public was placed in the sterile bottles. This method included not only tubercle bacilli that might have gained entrance at the dairy, but also any that might have gained entrance through the handling of milk by dealers suffering with tuberculosis. After collecting the samples they were brought immediately to the laboratory for examination.

METHODS OF ANALYSIS.

It was thought advisable to make an examination and estimate the percentages of fat, acid, total solids, and leucocyte and bacterial contents of the milk, in addition to determining the presence of streptococci and tubercle bacilli, as these data indicate approximately the quality of the milk and the care taken in its production.

The percentage of fat was determined by the Babcock method. The percentage of acid was determined by a one-tenth normal solution of sodium hydrate.

The percentage of total solids was estimated by the use of the following formula: lactometer+1.2Xfat=per cent of total solids. The specific gravity was determined by using Quevenne's lactometer.

The number of leucocytes was estimated by the Doane-Buckley method.

Agar-agar plates were used in determining the number of bacteria per cubic centimeter. The plates were placed in the incubator for twenty-four hours at 37° C. and at room temperature (26° C.) for twenty-four hours before the counts were made.

TECHNIC USED IN DETERMINING THE PRESENCE OF STREPTOCOCCI AND TUBERCLE BACILLI.

In brief, the technic used in determining the presence of streptococci and tubercle bacilli in the milk was as follows: Ten cubic centimeters of a thoroughly mixed sample was placed in each of three centrifuge tubes by means of a sterile pipette. These were placed in an ordinary electric centrifuge and run for thirty minutes at approximately 1,200 revolutions a minute. The tubes were then taken from the centrifuge and by means of a sterile wire loop the cream. was removed and placed in a sterile crucible. Sterile water was added to the cream to bring the volume up to 3 c. c. and to make a suitable emulsion for inoculation. The milk remaining in the centrifuge was then drawn off with a sterile pipette down to the 1 c. c. mark. The 1 c. c. of sediment in each of the three tubes was placed in another sterile crucible. Several slides from both the cream and the sediment were examined carefully under the microscope for the presence of streptococci and tubercle bacilli.

For the first 16 samples only 2 guinea pigs were inoculated, one receiving the 3 c. c. of cream emulsion, the other the 3 c. c. of sediment. For the remaining samples 3 guinea pigs were used; one received 2 c. c. of the cream emulsion, one 2 c. c. of the sediment, and another a mixture of 1 c. c. of the cream emulsion and 1 c. c. of the sediment. Thus in every instance each guinea pig was inoculated with a volume of 2 c. c., except in the first 16 samples, where a volume of 3 c. c. was used.

The guinea pigs were all inoculated subcutaneously, as this is considered the best method where milk is suspected of containing tubercle bacilli. The reason for this is that when guinea pigs are inoculated intraperitoneally a large percentage usually die of septic peritonitis before tuberculosis has time to develop. When inoculated subcu

taneously other infection is less liable to kill the animal, and the tubercle bacilli, if present in the sample, may manifest themselves in the lymph nodes.

EXAMINATION OF ORDINARY MARKET MILK.

The results of the estimations of the percentages of fat, acid, total solids, the specific gravity, and the leucocyte and bacterial contents are tabulated in Table 1. The data in this table show that in many instances the milk was of a poor quality. The bacterial count indicates that very little care had been taken in the production and handling of the milk. The wide variation in the bacterial content may be partially explained by the fact that the age of the milk varied. Table 1.—Results of examination of samples of ordinary market milk obtained from dealers in Philadelphia.