BACILLUS OF TUBERCULOSIS. 309 



Always make two cover-glass preparations from each 

 specimen. Report no result as negative until at least 

 two preparations have been subjected to a thorough 

 search with a 1/12 oil-immersion or 2 mm. apochromatic 

 lens by means of a mechanical stage. From a very 

 large experience in the examination of sputum for 

 tubercle bacilli, the New York Health Department 

 bacteriologists have concluded that the examination 

 of two preparations of each specimen in the careful 

 manner described above is usually sufficient to demon- 

 strate the presence of the bacilli when they are pres- 

 ent in the sputa, and they are usually found to be 

 present to this extent in fairly well-developed cases 

 of pulmonary tuberculosis, and in many cases which 

 are in the incipient stage. There are, however, un- 

 doubted cases of incipient pulmonary tuberculosis which 

 require the examination of many preparations before 

 the tubercle bacillus can be found; and that cases also 

 occur in which the sputum for a time does not contain the 

 bacilli, which were, nevertheless, present at an earlier 

 period, and which again later appear. Therefore, if cases 

 occur which may be still regarded as possibly tubercu- 

 losis, further examinations of the sputum should be 

 made. It should also be constantly borne in mind 

 that the demonstration of the presence of tubercle 

 bacilli in the sputum proves about as conclusively as 

 anything can the existence of some degree of tubercu- 

 losis; but that the absence of tubercle bacilli or the 

 failure to find them microscopically does not positively 

 exclude the existence of the disease. Here injections 

 of tuberculin can be made use of. 



