294 BACTERIA PATHOGENIC TO MAN 



By keeping the tubes inclined no undue amount of condensation of 

 water can collect in the bottom, and the upper portion of the serum 

 remains moist. The only precaution to be applied to prevent infection 

 with moulds is to thoroughly flame the joint between the tube and cap, 

 as well as the plugged end, before opening the tube/' 



In our experience, when cultures are made exactly according to the 

 above directions, a growth is usually obtained, but Dorset advises the 

 use of an egg medium. Many, including ourselves, have had good 

 results with it. It is more difficult to get a growth of bovine than of 

 the human type of bacilli. All methods frequently fail when the 

 tuberculous tissue used contains very few bacilli. 



Pathogenesis. The tubercle bacillus is pathogenic not only to man, 

 but to a large number of animals, such as the monkey, pig, cow, cat, 

 etc. Guinea-pigs are extremely susceptible, and are much used for 

 the detection of tubercle bacilli in suspected material. When inoculated 

 with the minutest doses of the living bacilli they usually succumb to 

 the disease. Infection is most rapidly produced by intraperitoneal 

 injection. If a large dose is given death follows in from ten to twenty 

 days. The omentum is found to be clumped together in sausage-like 

 masses and converted into hard knots, which contain many bacilli. 

 There is no serous fluid in the peritoneal cavity, but generally in both 

 pleural sacs. The spleen is enlarged, and it, as well as the liver and 

 peritoneum, contains large numbers of tubercle bacilli. If smaller 

 doses are given the disease is prolonged. The peritoneum and interior 

 organs spleen, liver, etc. are then filled with tubercles. On sub- 

 cutaneous injection, for instance, into the abdominal wall, there is a 

 thickening of the tissues about the point of inoculation, which breaks 

 down in one to three weeks and leaves a sluggish ulcer covered with 

 cheesy material. The neighboring lymph glands are swollen, and at 

 the end of two or three weeks may attain the size of hazel-nuts. Soon 

 an irregular fever is set up, and the animal becomes emaciated, usually 

 dying within four to eight weeks. If the injected material contained 

 only a small number of bacilli the wound at the point of inoculation 

 may heal up and death be postponed for a long time. On autopsy the 

 lymphatic glands are found to have undergone cheesy degeneration; 

 the spleen is very much enlarged, and throughout its substance, which 

 is colored dark red, are distributed masses of nodules. The liver is 

 also enormously increased in size, streaked brown and yellow, and the 

 lungs are filled with grayish-white tubercles; but, as a rule, the kidneys 

 contain no nodules. Tubercle bacilli are always found in the affected 

 tissues, but the more chronic the process the fewer the bacilli that are 

 apt to be present. 



Rabbits are also quite susceptible to tuberculosis, but considerably less 

 so than guinea-pigs. In rabbits death almost invariably follows inocu- 

 lations of tuberculous material into the anterior chamber of the eye. 

 The local effects are iris tuberculosis and cheesy degeneration of the 

 pupil. The bacilli then penetrate to the neighboring lymph glands, 

 producing softening of these, then pulmonary tuberculosis, general 



