TUBERCLE 75 



numbers, a local swelling will usually appear in about ten days, and 

 in a week or two more the lymph-glands (at first those appropriate to 

 the region, at a later date the internal ones), and the liver and spleen 

 will be affected. The animal may be killed and examined in three 

 weeks : the appearances are as a rule quite characteristic, but smears 

 should be made from the lesions and examined for tubercle bacilli in 

 the ordinary way. Sections may also be cut. 



Cultural Methods. The tubercle bacillus grows very slowly on 

 artificial media. Of these the best are Dorset's egg medium and 

 glycerinated blood-serum (coagulated). Dorset's medium is pre- 

 pared by emptying the contents of fresh eggs into a sterile flask, using 

 all aseptic precautions : adding normal saline in the proportion of 

 one part to three of egg : shaking well so as to mix thoroughly the 

 yolk, white, and salt-solution : filtering through sterile muslin : plac- 

 ing the result in tubes, which are sloped and coagulated at 80 C. in 

 the usual way. Glycerinated blood-serum is made by adding 4 per cent, 

 of glycerin to chloroformed blood-serum. The mixture is then dis- 

 tributed into tubes, which are then sloped and coagulated in the manner 

 described for simple blood-serum. Glucose (2 per cent.) and peptone 

 (i per cent.) may also be added with advantage. 



The material for inoculation may be taken direct from the body, 

 if no other organisms are present (glands removed at operation, pus 

 from cold abscesses opened aseptically, etc.). In most cases, how- 

 ever, especially in dealing with sputum or urine, there are numerous 

 other microbes which would rapidly outgrow the tubercle bacillus. 

 Here we must either inject a guinea-pig, wait three or four weeks, 

 and make cultures from the internal organs or glands, or treat the 

 material with antiformin in the manner described above (taking care 

 not to allow the action to go on too far, or the bacilli might be 

 killed, and to use all aseptic precautions in the subsequent washing, 

 etc.), and inoculate culture tubes with the residue. To prevent the 

 tubes from drying up, they must be covered with indiarubber caps or 

 the cotton-wool plugs dipped into melted paraffin. Several should be 

 prepared from each case, as the organism does not grow easily in 

 primary cultures, and contaminations occur occasionally in spite of 

 all precautions. 



Growth occurs only between 30 C. and 42 C., and is best at 37 C. 

 As a rule it is not noticeable for about a fortnight, and subsequently 

 takgs the form of small, whitish scales. In subcultures the growth 

 is more abundant, and forms a wrinkled film with a dull white or 

 brownish surface, not unlike some species of lichen. Growth pro- 

 gresses slowly, and cultures remain alive for months. 



Types of Bacilli. Three types of bacilli, the human, bovine, and 

 avian, occur, but authorities have not yet decided whether they are to 

 be regarded as varieties of the same species, modified by their environ- 

 ment, or different species altogether : probably the former view is 

 more correct, as intermedfate forms occur, and the characters of any 



