IMMUNITY AGAINST MICROBES. 423 



all of the same length and thickness ; these differences in size 

 being due partly to an actual difference in size^ partly to two 

 or more being joined together, and possibly to the fact that 

 some are placed more or less obliquely in the preparation. 

 None show any signs of degeneration whatever. 



The appearance of the intra-cellular bacilli is very different. 

 A large number are, to all appearances, quite healthy, stain uni- 

 formly, and are of normal size or shape. Here and there, how- 

 ever, an intra-cellular bacillus is found which, instead of stain- 

 ing as deeply as the others, assumes a light purple tinge. This 

 tint may be perfectly uniform, but at other times part only of 

 the bacillus is stained of a dark purple colour, whilst other 

 parts of the same micro-organism assume a lighter shade, and 

 the most varied forms of degeneration can be observed. 



Sometimes the centre of the bacillus takes up the colouring 

 matter badly, whilst the periphery still stains deeply. The 

 micro-organism then consists of a central, badly staining core, 

 and a dark, deeply staining sheath (see figs. B 3, 6, B 5, c). 

 Sometimes one edge only of the micro-organism retains the 

 colouring matter deeply, whilst the remainder assumes a light 

 purple colour (fig. B 5, b). In another stage the whole 

 bacillus is of a uniform pale purple hue, owing to the gradual 

 breaking up and disappearance of the colouring matter in the 

 sheath. 



In other bacilli the degeneration, marked by the loss of 

 power of fixing the colouring substance, begins at the peri- 

 phery of the micro-organism, the centre still retaining the 

 colouring matter, while the edges remain unstained. The 

 central coloured part becomes less and less in amount, so 

 that at last a small streak of it only is left. Later on the 

 central part itself breaks up, and forms a very thin, inter- 

 rupted, irregular streak lying in the interior of a bacillus. 



The process of degeneration in other bacilli affects the whole 

 breadth of the bacillus uniformly. One end of the bacillus 

 stains normally, whilst the other is of a pale homogeneous 

 colour (see fig. B 4, 6). Sometimes an intra-cellular bacillus 

 consists of a row of dots staining darkly, and embedded in a 



