522 Transactions of the Society. 



ordinary bacteriological preparations, the broken parts of colonies 

 will present a hopeless confusion. It is simply due to these methods 

 of preparation that the fact has not hitherto been recognized 

 that by far the greater proportion of the white deposit consists of 

 colonies of this highly organized bacterium or parasitic alga. The 

 easiest way to obtain unbroken colonies, or well-preserved portions 

 of large colonies, is from extracted teeth. Part of the tartar 

 ridge not disturbed by the forceps should be chosen, and some of 

 the Leptothrix from the surface gently scraped off with a needle, 

 and transferred to a drop of Locke's solution, or one of half Locke 

 and half Gram's iodine, on a slide. If too thick a lamp, it may 

 be divided with a needle into smaller portions, and a cover-slip 

 then gently pressed down to flatten out the preparation sufficiently 

 to examine it. It must be remembered that the colonies have 

 often been broken and disturbed whilst still in the mouth, unless 

 they are in a sheltered position such as in a pyorrhoea pocket, from 

 which beautiful little free colonies may sometimes be obtained. 

 Balls of Leptothrix colonies pressed out from the tonsil-crypts 

 also provide excellent unbroken material. To make permanent 

 preparations of Leptothrix, portions of colonies should be carefully 

 selected in Locke's solution or saliva under a dissecting microscope; 

 they should then be arranged in a drop on one cover-slip and 

 another pressed gently on top, and the whole immersed com- 

 pletely in some fixing solution, preferably freshly-made Carnoy or 

 Schaudinn, and left there for about ten minutes, after which the 

 cover-slips should be gently separated. One or other of them will 

 probably show fairly good clumps fixed in a flattened condition. 

 We have found Stephens' ink the best stain for colonies fixed 

 in this way ; and, for small separated branches, Giemsa or iron- 

 hsematoxylin (long method). 



Leptothrix colonies vary immensely, but a fairly typical speci- 

 men of a small unattached well-developed colony (fig. 15) shows 

 the following structure. The centre of the colony is a nodule of 

 hard tartar, from which radiate bundles of long coarse threads 

 divided into segments of variable lengtli, which usually give a 

 reddish-purple reaction with Gram's iodine (fig. 18). The ground- 

 work between these bundles is filled in with granular or coccoid 

 forms and traversed by numerous finer threads, most of which do 

 not give the iodine reaction. We have never observed any true 



EXPLANATION OF PLATE XV. 



The magnifications stated for the following figures, Nos. 15-21, are approximate. 

 Figs. 15, 16, 17, IS, 20 and 21 represent optical sections. Figs. 17 and 20 

 show Leptothrix colonies flattened under cover-slips. 



Fig. 15. — Diagram of a portion of Leptothrix colony, stained with iodine, which 

 shows up the coarse bundles of threads, x 425. 

 ,, 16. — Diagram of a " bottle-brush " branch, x 2000. 



