66 



THE PERMANENT FORMS, OR SPORES. 



low heat-conducting power, and a very slight degree of perme- 

 ability by noxious substances. This latter opinion seems the more 

 probable one, considered from a physical point of view, and is 

 further supported by 



54. The Behaviour of the Endospores towards Dyes. 



As already observed in a previous chapter, the dead plasma of 

 the bacterial cell absorbs colouring matters greedily and copiously. 

 The staining of the endospores is, however, more difficult, and 

 consequently they have to be exposed to the dye a much longer 

 time before they will absorb any of it. 

 However, the colour thus taken up is re- 

 tained by them more firmly than by the 

 vegetative forms. 



This property has been utilised in micro- 

 scopy to obtain a differential staining of 

 the spore-bearing bacterial cells, for which 

 purpose the latter are treated with a suit- 

 able (e.g. red) colour solution until the 

 spores are thoroughly impregnated there- 

 with, the preparation being then steeped 

 in a decolorising liquid (generally slightly 

 acidified alcohol), wherein it is left until 

 the vegetative cells are deprived of the 

 colour. These latter are thereafter stained 

 anew by a short immersion in a second 

 colour (e.g. blue) solution, a two-colour 

 preparation (double-staining) being thus 

 obtained, the spores in this case being red 

 and the rods blue. More detailed directions 



for double-staining will be found in Hueppe's handbook, Eisenberg's 

 treatise, and in Bernheim's Taschenbucli (Pocket-book). Fig. 20 

 gives a black and white reproduction of a cover-glass preparation 

 of spore-bearing Jlacillus subtilis stained only once, so that the 

 spores are unchanged, and appear colourless (white). 



The aforesaid behaviour of bacterial endospores towards colour- 

 ing matters is characteristic of all. From this fact it is not 

 infrequently, though erroneously, assumed by medical bacterio- 

 logists that any formation, in the interior of the cell, that behaves 

 similarly towards dyes is to be considered as an endospore ; whereas 

 it is not yet proved that spores alone exhibit this power. A general 

 report concerning the spore formation in any bacillus must there- 

 fore be received with due reserve when it rests merely on the 

 result of staining experiments. The sole decisive proof of the 

 sporous nature of such bodies is afforded by their germinating 

 power alone, a subject discussed in the next chapter. When this 

 property has been observed, the staining flask is no longer needed, 



FIG. 20. Bacillus subtilis. 



Cover - glass preparation 

 from an eight days' old 

 gelatin culture grown 

 at room temperature. 

 Stained with Vesuvine. 

 The spores, not having 

 absorbed the dye, show 

 up as white specks 

 against the (dark - 



. stained) vegetative 

 cells. (After Baum- 

 garten.) Magn. 950. 



