ASSIMILATION AND NUTRITION, 



167 



at eventide :* and from the florets of the elegant anthoxanthum odora- 

 tum^ or spring-grass, that we are chiefly furnished with the sweet and fra- 

 grant scent of new-mown hay. But occasionally the odours thus secreted 

 are as intolerable as any that are emitted from the animal world ; of 

 which the ferula assafcBtida^ or assafetida plant, and the stapelia hirsuta, 

 or carrion flower, are suflScient examples. 



To the same secernent powers, moreover, of animals and vegetables, 

 existing in particular organs rather than extended through the system ge- 

 nerally, we are indebted for a variety of very valuable materials in trade 

 and diet, as gums, resins, wax, fat, oils, spermaceti. And to the same 

 cause we owe, also, a production of a multiplicity of poisons and other de- 

 leterious substances : such, for instance, as the poison of venomous ser- 

 pents, which is found to consist of a genuine gum, and is the only gum 

 known to be secreted by animal organs ; the electric gas of the gym- 

 notus electricus and raia Torpedo ; the pungent sting of the stinging-net- 

 tle, urtica urens^ and of the bee, both which are produced from a struc- 

 ture of a similar kind ; for every aculeus or stinging point of the nettle is 

 a minute and highly irritable duct, that leads to a minute and highly irri- 

 table bulb, filled with a minute drop of very acrid fluid : and hence, when- 

 ever any substance presses against any of the aculei or stinging points of 

 the plant, the impression is communicated to the bulb, which instanta- 

 neously contracts, and throws forth the minute drop of acrid fluid through 

 the ducts upon the substance that touches them. 



As the secernent system thus evidently allots particular organs for the 

 secretion of particular materials, the absorbent system is in hke manner 

 only capable of imbibing and introducing into the general frame particu- 

 lar materials in particular parts of it. Thus, opium and alkohol, the juice 

 of aconite, and essential oil of laurel or bitter almonds, produce little or 

 no effect upon the absorbents of the skin, but a very considerable effect 

 upon the coating of the stomach. In like manner, carbonic acid gas in- 

 vigorates rather than injures, when applied to the absorbents of the sto- 

 mach, but instantly destroys life when applied to those of the lungs ; while 

 the aroma of the toxicaria Macasariensis^ or Boa upas, of which we 

 have heard so much of late years, proves equally a poison, whether re- 

 ceived by t«ie skin, the stomach, or the lungs. 



So, also, substances that are poisonous to one tribe of animals are me- 

 dicinal to a second, and even highly nutritive to a third. Thus, swine 

 are poisoned by pepper-seeds, which to a man are a serviceable and grate- 

 ful spice ; while henbane-roots, which destroy mankind, prove a whole- 

 some diet to swine. In like manner, aloes, which to our own kind is a 

 useful medicine, is a rank venom to dogs and foxes ; and the horse, which 

 is poisoned h - the phellandrum aquaticum^ or water-hemlock, and corro- 

 sive sublimate, will take a dram of arsenic daily, and improve hereby both 

 in his coat and condition. 



It has already appeared, that the secernent vessels of any part of the 

 system, in order to accomplish a beneficial purpose, as, for example, that 

 of restoring a destroyed or injured portion of an organ, may change their 

 action, and secrete a material of a new nature and character. An equal 

 change is not unfrequently produced under a morbid habit, and the se- 

 cretion will then be of a deleterious instead of being of a healthy and 

 sanative kind. And hence, under the influence of definite causes, tlie 



* Hookers Monography of British Jungerm, 



