SPONGIA OFFICINALIS. 



sponge, rooted to the rock, seems absolutely incapable of this 

 function, and the most microscopic scrutiny has failed to detect 

 its existence. 



The best definition of an animal, as distinguished from a 

 vegetable, which has as yet been given, is, that whereas the 

 latter, fixed in the soil by roots, or immersed perpetually in the 

 fluid from which it derives its nourishment, absorbs by its 

 whole surface the nutriment which it requires ; the animal, be- 

 ing generally in a greater or less degree capable of changing 

 its position, is provided with an internal receptacle for food, 

 or stomachal cavity, from which, after undergoing the process 

 of digestion, the nutritious matter is taken up. But in the 

 case of the sponge no such reservoir is found ; and in its 

 place are only anastomosing canals which permeate the whole 

 body, and convey the circumambient medium to all parts of 

 the porous mass. 



Another circumstance which specially appertains to the ani- 

 mal kingdom is derived from the chemical composition of or- 

 ganized bodies. Vegetables contain but a small proportion of 

 azote in their substance, whilst in animals this element exists 

 in considerable abundance, causing their tissues, when burned, 

 to give out a peculiar odor, resembling that of burned horn, 

 and in this particular sponges differ from vegetable matter, 

 The discoveries of Mr. Bowerbank appear conclusive as to 

 its animality. In one species of the sponge he detects a 

 branched vascular system, with globules in the vessels anal- 

 ogous to the circular blood disks of the higher animals. 

 Nothing analogous to this has hitherto been detected in plants. 



The common sponge of commerce is made up of horny, 

 elastic fibres of great delicacy, united with each other in every 

 possible direction, so as to form innumerable canals, which 

 traverse its substance in all directions. To this structure the 

 sponge owes its useful properties, the resiliency of the fibres 

 composing it making them, after compression, return to their 

 former state, and leaving the canals which they form open, 

 to suck up surrounding fluids by capillary attraction. 



The dried sponge is, however, only the skeleton of the liv- 

 ing animal ; in its original state, before it was withdrawn from 

 its native element, every filament of its substance was coated 

 over with a thin film of glairy semifluid matter, composed of 

 aggregated transparent globules, which was the living part of 

 the sponge, secreting, as it extended itself, the horny fibres 



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