1899] MICROSCOPICAL JOURNAL 95 



them the most sensitive of all. Any increase in the 

 saltness of the water would produce a change in the ar- 

 rangement and color of the endochrome in a short time. 



I had a quantity of these Pleurosigma in a small 

 tumbler on my worktable. They were left here in a warm 

 room over night. The next day the water had dried 

 down to less than half its former bulk and the diatoms, 

 showed a remarkable change. The endochrome had 

 darkened in color and separated into detached masses gen- 

 erally six or eight in number but several were filled with 

 very small globular forms resembling spores. Their ac- 

 tivity had diminished, but most of them still retained 

 their characteristic motions. I applied a small drop of 

 fresh water to one edge of the cover-glass. All motion 

 was instantly arrested, and those diatoms directly in the 

 line of flow had about half their endochrome forced out 

 into the water, apparently through the raphe, while in 

 those out of the direct current, the endochrome soon 

 swelled and became apparently homogeneous, filling the 

 frustule. Afterwards their motions gradually recom- 

 menced and they were soon traveling again nearly as 

 fast as ever. 



I repeated this experiment many times, and always 

 with the same result. All these actively traveling Pleu- 

 rosigma had invariably a small bubble of air inside, in 

 contact with the valve at the raphe. The position of this 

 air bubble varied definitely for each species. In P. amer- 

 icanum it was near the centre of the flexure, in P. hypo- 

 campus it was nearer the end, and in N. sigma it was at 

 the point of the frustule. After it had once attracted 

 my attention, I did not fail to find it in every case. 



Card. — Qualitative, Quantitative and microscopical urin- 

 alyses, urinary calculi, gonococcus, urine for diagnosis of 

 typhoid, sputum for bacillus tuberculosis,analysis of water, 

 vinegar, milk, tests for arsenic in wallpaper, etc. — W. H. 

 Ohler, Portland, Me. 



