124 THE MECHANISM OF LIFE 



gas in a balloon. This pressure increases the volume of the 

 cell, and in consequence water rushes in through the permeable 

 membrane aid still further distends the cell. Most beautiful 

 osmotic cells may be produced by dropping a fragment of 

 fused calcium chloride into a saturated solution of potassium 

 carbonate or tribasic potassium phosphate, the calcium 

 chloride becoming surrounded bv an osmotic membrane of 

 calcium carbonate or calcium phosphate. This mineral 

 membrane is beautifully transparent and perfectly extensible. 

 It is astonishing to contemplate the contrast between the 

 hard crystalline forms of ordinary chalk and these soft tran- 

 sparent elastic membranes which have the same chemical 

 constitution. These osmotic cells of carbonate of lime or 

 phosphate of lime consist of a transparent membrane enclosing 

 liquid contents and a solid nucleus of chloride of calcium. 

 Their form is that of an ovoid or flattened sphere, and they 

 may attain a diameter of seven centimetres or more. 



.More frequently the osmotic growth consists of a number 

 of cells instead of one large cell. The first cell gives birth to 

 a second cell or vesicle, and this to a third, and so on, so that 

 we finally obtain an association of microscopic cellular cavities, 

 separated bv osmotic walls — a structure completely analogous 

 to that which we meet with in a living organism. 



We may easily picture to ourselves the mechanism by 

 which an osmotic cell gives birth to such a colony of 

 microscopic vesicles. The membrauogenous substance, the 

 chloride of calcium, diffuses uniformly on all sides from the 

 solid nucleus, and forms an osmotic membrane where it comes 

 into contact with the solution. This spherical membrane is 

 extended bv osmotic pressure, and grows gradually larger. 

 Since the area of the surface of a sphere increases as the square 

 of its radius, when the cell has grown to twice its original 

 diameter, each square centimetre of the membrane will receive 

 by diffusion but a quarter as much of the membraiiogenous 

 substance. Hence, after a time, the membrane will not be 

 sufficiently nourished bv the membranogenous substance, 

 it will break down, and an aperture will occur through which 

 the interior liquid oozes out, forming in its turn a new 



