28 RAINEYj ON CARBONATE OF LIME GLOBULES. 



on the supposition that the increments which each globule 

 received in equal spaces of time are equal, but as the filling 

 in of this space takes place more slowly as the globules in 

 these experiments get nearer together, the degree of minute- 

 ness of the particles in question would far exceed that above 

 mentioned. In this case, their size, when the globules were 

 on the point of actual contact, would be several thousand 

 times smaller than that of the smallest particle of matter 

 visible by any known power of the microscope. But how- 

 ever small these particles are, they have, doubtless, a defi- 

 nite size, otherwise the surface of the increasing globules 

 would, most probably, not be so sharply defined, but gradually 

 shaded off. Besides, it can be shown, by dissolving out the 

 earthy component, and leaving the gum one, that the layer 

 of a globule last formed is the densest. For this purpose, it 

 is only necessary to put the slides on which these globules 

 have been deposited into a solution of gum, which, either 

 being itself an acid or from the free acid it contains, 

 gradually dissolves out all the carbonate with efferves- 

 cence, and leaves the gum-element insoluble, and more or 

 less of the form of the original globule, this depending 

 very much upon the relative quantity of gum in com- 

 bination with the earthy matter. Hence the globules 

 which have been made in a strong solution of gum are 

 the best for demonstrating this fact, and those made in 

 the bottles according to the first process are necessary for this 

 experiment. The gum-constituent, thus prepared, presents 

 under the microscope the appearance of a nucleated cell ; but 

 that which appears to be a nucleus is rather a vacuity, and in 

 these globules, when examined by the microscope by 

 polarized light, in which the carbonate is only partially re- 

 moved, the central part is generally dark, without having a 

 cross, showing either a very small quantity or a total absence 

 of the carbonate of lime. In many globules thus treated the 

 exterior gum-layer appears quite like a dense husk, enclosing 

 the parts within. These gum-residua, being insoluble, can 

 be kept in glycerine, but if any of the carbonate had been 

 left in them it becomes gradually removed. I have noticed 

 in my paper on the dental tissues the same fact taking place 

 in the calcareous globules of a delicate film of calcifying 

 oyster-shell. Now, two facts are obvious from these expe- 

 riments — one is, that the particles of gum and carbonate of 

 lime are combined in these globules in inconceivably minute 

 quantities ; and the other, that the gum becomes insoluble 

 in water. In these respects, gum in plants bears an analogy 

 to albumen in animals. With respect to the globular form 



