420 BACTERIA OF THE SPUTA 



dentaria and its treatment with the aniline colours, or with the 

 solution of iodine, there is little to add to what has been said in 

 the previous Memoir. We gave there the precise rules, in order 

 to obtain from the patina dentaria the greatest possible number of 

 fructifications, taking it before a meal or early in the morning. 

 We found afterwards that the fructifications are more abundant on 

 teeth with a thin film of tartar, particularly in the superior eye- 

 teeth. About the disintegration and colouring of the clods we 

 refer to what has been said. For the acidulated solution of iodine, 

 we placed on the slide, first, a small drop of lactic acid, disin- 

 tegrating in it afterwards the patina, and lastly adding to it one or 

 two drops of solution of iodine. It generally takes a quarter of 

 an hour to get a proper colouring. 



In the preceding Memoir we suggested that the superfluous 

 liquid should be allowed to trickle down from the sides, after 

 applying the cover-glass ; but afterwards we discovered that it was 

 better to let most of the liquid evaporate before applying the 

 cover-glass, so as to avoid the wave of liquid caused by the pres- 

 sure, which might remove many bacteria and bacilli and several 

 isolated filaments and clusters set free from the tiny islands that 

 often supply the most instructive specimens ; blotting paper would 

 also take up many of the specimens. To eliminate the air-bubbles 

 keep the cover-glass on edge (straight up) with the two first fingers 

 of the left hand, so as to form an acute angle with the slide, at 

 two centimetres from the preparation ; then with a straight needle, 

 held in the right hand to support the glass, and with a bent needle 

 pushing it on the specimen, lower it down gently on to the edge of 

 the preparation, when the air-bubbles will be set free. 



If we wish to institute a comparison between the two stains 

 adopted in this work, we may say that gentian violet colours 

 briskly the little spores, but at the same time attacks and obscures 

 the viscid substance, so that, wherever it fully invests, the peduncles 

 or sterigmata are either not seen at all, or may hardly be distin- 

 guished. This happens even by applying very little tint. Never- 

 theless isolated fructifications slightly affected by the tint may some- 

 times be found in the preparation, and it is just upon one of these 

 occasions that we first detected the peduncles in question. For 

 this reason, the whole image, either of the single fructifications, or 



