520 G. H. DKEW. 



particles precipitated could not be ascertained, as the size varied 

 largely in cultures made at the same time, in the same media, and 

 kept apparently under the same conditions. The addition of Mag- 

 nesium tartrate in small quantities (0*2 grammes per 1000 c.c.) to 

 the culture media seemed to induce the precipitation of larger par- 

 ticles, but it did not appreciably affect the rate of growth of the 

 bacteria. 



In some of the older cultures that had been kept for a 

 week or more, the sides of the flasks were coated with a thin layer 

 consisting of extremely minute rhombohedral crystals of Calcium 

 carbonate. Occasionally these crystals formed around small bubbles 

 that had remained near the surface of the fluid, the weight of the 

 crystals eventually caused the bubbles to sink, and then the contained 

 gas became dissolved ; in this way a number of small hollow spheres 

 were formed, their walls consisting of minute crystals of Calcium 

 carbonate. The formation of these curious bodies occurred especially 

 readily in the Calcium succinate medium to which 0*2 grammes of 

 Magnesium tartrate per litre had been added. The deposition of 

 Calcium carbonate in a distinctly crystalline form was only noted in 

 old cultures, and then it was in an amount relatively extremely small 

 when compared to the precipitate of apparently amorphous Calcium 

 carbonate. 



Specimens of the precipitates from some of the culture media were 

 sent to Dr. Fred. E. Wright, of the Geophysical Laboratory of the 

 Carnegie Institution, who with great kindness examined them, and 

 described them as follows : — 



" Preparation I. Precipitate from medium composed of — 



" Contains two substances : (1) Fine grains of a strongly birefracting, 

 apparently uniaxial, optically negative substance, and with refractive 

 index about 1"66. This is probably calcite. The grains are isolated, 

 and no evidence of spherulitic crystallization was observed. On treat- 

 ment with very dilute Hydrochloric Acid, a noticeable evolution of 

 Carbon dioxide took place. (2) Scattered through the preparation are 



