276 



XXI. BACTERIA YEAST. 



interwoven with them. After addition of iodine solution the 

 thicker threads are coloured bluish-violet, the thinner ones yellow. 



The threads coloured blue 

 violet (by reason of their amy- 

 loid contents) are distinguished 

 as Bacillus buccalis, the others 

 as Leptothrix buccalis. The 

 iodine solution enables us to 

 see clearly a segmentation of 

 these threads into shorter 

 joints. The chains of four to 

 ten cells in a sheath, which 

 we observe now and again, 

 coloured blue violet with the 

 iodine, has been named Jodo- 



FIG. 102. Bacteria from the "fur" of coccus vulgaris. Then comes 

 teeth a BarMus buccalis and Leptothrix Spirochate dentium, in long 

 ouccalis, at a after treatment with iodine ; 



b, micrococcus ; c, Spirochcete dentium, after actively motile spirals (c) ; and 

 iodine ; d, Spirillum sputicienum (x 800). 1,1 o ?; j.- 



lastly Spirillum sputigenum, 



likewise actively motile, in " comma "-shaped rodlets often con- 

 nected in pairs (d). Besides these, are incidentally found in 

 the mouth a considerable number of other bacteria, in part as 

 yet insufficiently studied. These bacteria live saprophytically 

 upon the mucous membrane or the fur of the teeth, or on 

 fragments of food ; and some, at least, are concerned in pro- 

 moting the decay of teeth, in that they penetrate into the 

 calcined tissues of the teeth and destroy the softened bone. If 

 a preparation be treated with 10 per cent, solution of common 

 salt the bacteria are plasmolysed. This is best seen in the 

 thick threads of Bacillus buccalis. The contents of individual 

 cells of the rods are seen aggregated into one or more refrac- 

 tive masses, having quite the aspect of spores. At the same time 

 the wall becomes recognisable. If the preparation has been in 

 water for a little while a weaker solution, e.g., 5 per cent., will 

 induce plasmolysis. 



Spirochate plicatilis. If we have water in which Algae, espe- 

 cially Spirogyra and Vaucheria, are decaying, and examine a little 

 of this fluid, we shall find in it, almost to a certainty, motile, 

 exceedingly fine spiral threads (Fig. 103), like those already found 

 in fur of teeth, but much longer than they. These flexible cork- 

 screw-like threads rruove rapidly in the water. They turn on their 



