46 MEMOIR OF BARON HALLER. 



duced by the action of the heart : this net-work 

 commences as it were by points ; these points soon 

 become threads, which ere long are coloured, and 

 turn out to be arteries and veins, dividing at very 

 small angles. These angles enlarge ; whitish coloured 

 spaces appear between the vessels, which, with time, 

 dilate exactly like the spaces betwixt the fibres of 

 leaves. In retracing the successive changes of this 

 membrane, it would evidently appear that it had 

 always existed, as also its vessels ; that it had ex- 

 panded upon itself; that the impulse of blood had 

 prolonged the arteries, or divided its folds ; that it 

 had elongated the vessels from each other, and given 

 to the membrane its length and breadth, its colour- 

 less spaces, and even its solidity. I regard this 

 example as instructive, and calculated to exhibit 

 the shades by which a soft and semi-fluid substance 

 can pass into a state wholly different from its first 

 condition, by simple evolution. 



Regarding solidity, we have only to trace the 

 successive increase of the lungs and other internal 

 viscera, of the flesh, bones, &c. to perceive the steps 

 by which a true fluid may become viscid, may then 

 harden by insensible degrees, and this without the 

 mixture of any new parts. All these portions of 

 the young animal are produced from a fluid, appa- 

 rently organized, they then become consistent, and 

 gradually acquire well denned limits. We need 

 hot here dwell on the causes of these changes. TV r e 

 may simply remark, that a simple diminution of 

 the fluid narls, the effect of the dilatation of the 



