AND CONTENTS OF THE MOUTH. 83 



Another source of error, against which it is difficult to guard, 

 is the reflux of nasal mucus, through the posterior nares, in the 

 back of the mouth, and its successive expectoration mixed with 

 saliva. Naturally, ellipsoidal epithelia and myelin, even in such 

 sputa, are wanting. 



In any case the presence of the myelin and the ellipsoidal 

 epithelia induces us to regard the sputum as proceeding from the 

 air-passages. These are two important points when, for instance, 

 a doubt arises whether a sputum with a rusty appearance proceeds 

 from the nose or the chest ; as, in our daily researches on sputa, 

 we never detected ellipsoidal epithelia or myelin in spurious sputa ; 

 whilst in the genuine expectorations they are very seldom absent, 

 and when not found in the first, they appear in the second 

 preparations. 



We come now to the manner of collecting the sputa. 



The act of spitting is accomplished in two different efforts : 

 by the first, the genuine sputum, nearly entirely free from saliva, 

 and that which is required is coughed up ; but soon after by a 

 second effort, saliva is emitted with the residue of the sputum left 

 behind. This second sputum (being nearly all saliva) is elimin- 

 ated. In order to avoid mixing the sputum with saliva, the patient 

 should not keep it in the mouth too long. 



Instead of a spittoon, it is better to use a colourless plate or 

 saucer, perfectly clean, where the sputa can be kept separate, and 

 then selected for examination. The sputum should be taken at 

 the most viscid point with a bent needle or forceps, and raised so 

 that the saliva and the more fluid part of the mucus with which 

 it is mixed, may trickle down on the plate. What remains on the 

 instrument is quite sufficient for successive investigations, as it will 

 necessarily contain very little saliva. To preserve it, it should at 

 once be placed in a glass tube, which has previously been cleaned 

 with sulphuric acid, and washed out with alcohol. 



For the coloured preparations we have to modify the directions 

 given in the preceding work. It is better to keep the solution of 

 gentian violet separated from the aniline water, so as to prevent 

 decomposition ; but we must avoid putting the glass rod, still wet 

 with aniline water, into the colouring solution, and vice versa. 

 Two different rods must be used. With a small rod put first on 



