MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 21 



Once stained, they again differ from the parent cells in resisting 

 decolorisation ; this fact is taken advantage of to double-stain spore- 

 bearing bacilli (Fig. 7). 



In staining micro-organisms, the protoplasm is sometimes broken 

 up into irregular segments or granules, as in many spirilla, and we 

 may add the bacilli of tuberculosis and leprosy. The beaded 

 appearance of the tubercle bacillus is well known. Some observers 

 have regarded the beads, others the bright spaces between them, 

 as spores. But spores in unstained preparations appear as glistening 

 bodies with sharp contour. They do not stain at all, or very little, 

 by the ordinary processes. These considerations led the author to 

 stain and examine tubercular sputum and pure-cultures under 

 careful illumination, and with such lenses as Powell and Lealand's 

 -^ in. hom. imm. The tubercle bacillus in sputum (Fig. 8), as a rule, 



Fig. 8. — Bacilli of Tubekolb in Sputum, x 2500 (from photographs). 



consists of a very delicate sheath, holding together a number of 

 deeply stained granules, for the most part round or cylindrical, with 

 irregular contour, and differing considerably in size, while the light 

 interspaces are seen to vary in form according to ' the shape of the 

 granules. On the other hand, particularly in old cultures, more or 

 less spherical, sharply defined bodies are observed in the bacilli, and 

 also set free. These are the true spores of the tubercle bacillus, 

 and are quite distinct from the irregular granules. There can be 

 no doubt that a tubercle bacillus consists of a very delicate sheath, 

 with protoplasmic contents which have a great tendency to break 

 up or coagulate into little segments or roundish granules, partly 

 owing to their age and the conditions under which they , are growij, 

 and partly to the treatment they are subjected to in. making a 

 microscopical preparation. This does not always occur, for the 

 bacilli at times are not beaded, but are stained in their entirety. 

 In the leprosy bacilli a similar appearance occurs. In stained 



