'' MOLECULAR COALESCENCE/' ETC. 225 



nearly three quarters of an inch. After cooling, the tubes 

 were removed, and each was found plugged with firm clear 

 jelly, so as to be thoroughly water-tight. Six of these tubes 

 were next filled with a slightly alkaline solution of potassium 

 oxalate, and placed with plugged ends in a weak solution 

 (about 6 grs. to 1 oz.) of chloride of calcium, the level of the 

 solution in the tubes being much higher than the level of the 

 calcium solution. The plug of jelly was thus interposed be- 

 tween the two solutions, in the hope that, diffusion slowly 

 occurring, the results of the mutual decomposition of the 

 oxalate and calcium salt might be found after a time in the 

 jelly, a fair representative as far as consistence was con- 

 cerned of the casts of the kidney tubes. The experiment 

 was performed in a room of the average temperature of 57° 

 Fahr. 



On the second day the plugs were clouded with white de- 

 posit, and fragments removed from them were found to con- 

 tain a large number of crystalline and rounded forms, includ- 

 ing both octohedra and dumb-bells. 



The jirocess Avas then allowed to go on for three months, 

 till, on the 12th March, 1869, an entire and uninjured plug 

 was removed and submitted to careful examination. The 

 oxalic solution was still clear ; the calcium solution was 

 thickened with deposit of calcium oxalate, but the relative 

 levels of the solutions were unaltered. The plug was found 

 free from decomposition, and opaque Avith earthy deposit. 

 The deposit was not uniform, but somewhat stratified, form- 

 ing a layer of greatest density near the calcium solution, a 

 layer of less density with some opalescence near the oxalic 

 solution, and several intermediate layers of still less density, 

 with alternate spaces of extreme scantiness of deposit. 



Transverse sections of the plug were made at thirteen 

 points ; the sections were transferred to glass slides, melted 

 with the gentlest possible heat, and examined under the 

 microscope with the half-inch objective. For preservation 

 they were afterwards slightly dried at a gentle heat, and 

 mounted in a solution of Canada balsam in chloroform. In 

 this course of preparation it was found that, although a great 

 variety of forms were present in the several sections, one 

 only, the octohedron, was altered ; the rest remained for 

 many weeks unchanged, a point which was easily determined 

 by comparison with fine sections of subsequently prepared 

 plugs placed on slides without use of heat or balsam. 



To sum up the results of the examination of the thirteen 

 sections, it was found that the forms existing on the side of 

 the oxalate were very different from those on the side of the 



