THE TUBERCLE BACILLUS. 215 



less gaps are to be seen, which formerly were con- 

 sidered to be spores. At present this theory has been 

 given up by most bacteriologists, as there do not seem, 

 sufficient grounds for belief in it. 



There are certain difficulties which are met with in 

 connection with the culture of tubercle bacilli. Above 

 all, it requires great skill and practice on the part of 

 the experimenter to obtain a pure culture from the 

 original material. The method to be employed is 

 described here, although the student is not recom- 

 mended to attempt to prepare pure cultures from 

 tuberculous material, as it requires a great deal of 

 time, and the result is only very doubtful. 



First of all, some ox-blood serum must be obtained, 

 and allowed to solidify, in a slanting direction, in wide 

 test-tubes. It is a good plan to keep it for a day or 

 two in the incubator before using it, so as to make 

 sure that it is thoroughly sterilised. The next thing 

 is to procure a tuberculous animal ; as guinea-pigs 

 are very susceptible to tuberculosis, it is, as a rule, 

 very easy to find one that is affected, or at any rate 

 to induce the disease in one by inoculating it with 

 tuberculous sputum. Directly after death the animal 

 is immersed in alcohol, which is set alight, so that, as 

 a rule, the hair is thoroughly singed off, and the skin 

 sterilised to a certain extent, without the tubercle 

 bacilli in the interior of the animal being affected. 

 The skin is now cut through with sterilised scissors 



