112 



A. M. GLAUERT AND E. M. BRIEGER 



Fig. 1. Ultra-tliin section of avian tubercle bacilli embedded in methacryiate. The organisms are distorted. Note the 

 complex nuclear apparatus and large cytoplasmic granules. 110,000. 



If the original inoculum is viewed directly, without 

 sectioning, it is seen to consist mainly of short rods 

 with electron-dense polar bodies and a transparent, 

 structureless cytoplasm. After 24 hours' growth these 

 rods elongate and round bodies are clearly visible 

 within them. These bodies have distinct membranes 

 and it was suggested that they might correspond to 

 the segmentation spores of the Nocardia. 



Methacryiate. — Sections of the small, transparent 

 rods of the inoculum show that they have large 

 central light areas containing threads and granules, 

 the "nuclear apparatus". The cytoplasm, which 

 occupies a narrow peripheral zone, has a granular 

 structure, the granules ranging in size from 100 to 

 200 A. There is some evidence of the presence of 

 fine threads and membranes within the cytoplasm 

 but the cells are not sufficiently well preserved for 

 these to be accepted with any certainty. The cells 

 are obviously swollen and distorted and nothing 

 definite can be deduced concerning the nature of the 

 nuclear material. 



After 24 hours" incubation the rods of the inocu- 

 lum have elongated, the dense threads and granules 

 in the nuclear region have more complex configura- 

 tions and the cytoplasm is denser (fig. I). The cyto- 

 plasm still has a granular structure and in some 

 organisms there is also a scattering of larger granules 

 of 200 to 400 A diameter. A few of the organisms 

 are in process of dividing by binary fission to form 

 two daughter cells, each with its own nuclear appa- 

 ratus. 



At later stages in the development of the bacilli a 

 very different pattern of internal structure is seen. 

 Rows of round bodies are observed forming inside 

 the bacilli. These units have a finely granular struc- 

 ture of uniform density and are enclosed within a 

 definite limiting membrane. Their formation is 

 accompanied by an increase in the number and size 

 of the larger cytoplasmic granules. The bodies do not 

 appear to contain an organised nucleus and in the 

 early stages of their development the nuclear appara- 

 tus of the bacillus is still visible outside them. We inter- 

 preted these bodies as spores (3), although the later 

 stages of their reproduction will have to be followed 

 before their nature can be clearly established. In 

 structure and development they bear a remarkable 

 similarity to the spores of the ordinary bacteria 

 described by Chapman (4). 



Aralciite. — The study of similar organisms embed- 

 ded in Araldite is only in its early stages but certain 

 differences of structure have already been observed. 



As was stated earlier, most of the bacilli appear to 

 be far better preserved. The cell wall is no longer 

 separated from the cytoplasm and there is clear 

 evidence of a cytoplasmic membrane underlying the 

 cell wall (fig. 2). This membrane has proved to be 

 particularly elusive in studies of methacryiate sec- 

 tions. The fine limiting membranes of the developing 

 spores are also clearly seen and appear to be double 

 (fig. 3). There seems to be no doubt that these fine 

 membranes are seriously distorted during methacry- 

 iate embedding. 



