16 



OUTLINES OF BACTERIOLOGY 



healthy culture of Spirillum giganteum be examined microscopically 

 when one day old, the cells will be found quite full of these reserve 

 materials, but if the culture be examined after five or six days, it will 

 be seen that the amount has very considerably diminished, because the 

 spirillum had need of the reserve and consequently used it. The fat- 

 globules can be identified by their strongly refractive appearance, and 

 by their reactions, and can be further distinguished from the volutin- 

 spheres by the fact that methylene-blue stains the latter but not the 

 former. Volutin has also this further peculiarity, that when stained 

 with this reagent the central portion of the larger spheres is purple, 

 and the periphery blue in colour (Fig. 25i). Fat-globules and volutin 



Fig. 26. — Bac. tumesceus, showing fat globules. 



have also been found in several other species of bacteria, e.g. fat- 

 globules are almost always found in healthy cultures of Bac. tumescens 

 (Fig. 26) and Bac. tuberculosis, whilst volutin has been found in Bac. 

 alvei and in other bacteria. 



Another reserve material is the carbohydrate, glycogen, which, in 

 Bac. asterosporus, makes its appearance shortly before the formation 

 of spores. This substance is recognised on treat- 

 ment of the cells with iodine, when irregular bodies 

 of a very deep reddish-brown colour will be 

 observed, staining much more intensely than the 

 surrounding protoplasm' (Fig. 27). 



Another reserve material has been found in 

 some of those bacteria which excrete butyric acid. 

 This material appears just before the formation of 

 spores. It is probably allied to starch, for when 

 treated with iodine it, like starch, stains blue. 



Finally, we take the case of those bacteria that 

 are coloured. In some cases, as has been stated, 

 the colour lies inside the cells, the colouring matter being a product 

 resulting from the breaking down of protoplasm, which colouring 

 matter must therefore be included in a list of substances that can 

 be identified inside the cell. This concludes the list of substances 

 that may be identified by the use of the microscope. By taking into 

 account the results of chemical analyses of bacterial cultures, the 







o 



Fig. 27. — Bac. astero- 

 sporus, showing grains 

 of glycogen. Stained 

 with iodine. 



