236 THE AMERICAN MONTHLY [Aug. 



surrounding it, which fact would distinguish inert 

 matter in some cases, from living matter on the slide. 



When everything is in readiness as above outlined, 

 a slide is prepared in the manner previously stated. If 

 possible a single large living Navicula nobilis must be 

 retained in the field of views. If it happens that the 

 frustular face presenting the nodules and raphe are first 

 shown, the attention may be directed attentively to the 

 median nodule, when it is strongly probable that there 

 will be seen at that point granules of India ink collecting 

 and massing together, and rising upwards, then dispersed 

 or carried away to the sides. At the same moment 

 along the median line of the raphe an interrupted or 

 continuous stream of granules of India ink will be seen 

 traversing the raphe. As the granules retreat along the 

 raphe, after having passed the nodular cavity, and when 

 near the posterior or passive end of the diatom as then 

 moving, the line of granules will be seen to be deflected 

 from the raphe, and to pour into a cloudlet-like mass on 

 one side of the passive end of the diatom. This phe- 

 nomenon may be watched during the whole period of 

 transit of the diatom. The action is sometimes intermit- 

 tent and sometimes continuous for a short period; but 

 no matter how long these motile appearances may be 

 studied, a proper interpretation of them could not be 

 readily had were it not for the fact that the diatom very 

 often turns over from the valvular aspect (side view) to 

 present its sutural face or front view, when the motile 

 phases of the running carbon granules present an entirely 

 diff"erent appearance. 



This allows the phases anteriorly noted, to be duly 

 interpreted, for as soon as, or very soon after the diatom 

 turns over, there will be observed, inverted into the 

 nodular cavities two solid lines of India ink granules, 

 which are sometimes very sharply defined and are as 

 clearly shown as if drawn with a pen and black ink on 



