in Orgamzed Beings. 107 



bon is exhaled in considerable quantity from the skin for a cer- 

 tain period after death, pei-spiration has appeared on the skin, 

 urine has been secreted into the bladder, and it is even said 

 that the hair has grown. It is only when these excretions are 

 finally stopped by the want of circulation, respiration, and 

 other vital functions, that decomposition can properly be said 

 to commence. 



With regard to the exci'etory functions of the lower classes 

 of plants and animals, we have very little certain knowledge. 

 The general surface in them seems to answer all the required 

 purposes ; and the first organs of secretion we can detect in , 

 animals seem rather appendages to the digestive apparatus 

 than parts of the excretory system. Though some may re- 

 gard the function of respiration in a distinct light, I see no 

 reason for considering it as anything else than a part of the 

 series of changes by which superfluous matter is discharged 

 from the system. Our present knowledge of the elementary- 

 structure of glands reduces the lungs to the same type with the 

 liver or kidneys ; both consist of an excretory duct upon the 

 minute ramifications of which bloodvessels are distributed, 

 a part of whose contents find their way throvigh the permeable 

 membrane which forms the tubes or cells ; and the branches, 

 although possessing a different form, have evidently the same 

 " fundamental unity" of structure. In regard to their func- 

 tions also, there would seem no further difference than this, 

 that whilst the excretion by the lungs serves an important pur- 

 pose, the maintenance of animal heat, that of the liver answers 

 another object by giving assistance in the digestive process. 

 Both have alike for their object the excretion of carbon from 

 the system, and their functions may pei'haps be regarded as in 

 some degree vicarious. 



The respiratory organs are found specially developed both 

 in plants and animals, as soon as a particular part of the sur- 

 face is set apart for absorption ; and the fluid is brought to 

 them by the circulating system before being applied to the ge- 

 neral purposes of nutrition. In plants we always find them 

 formed by expansions of the external surface, beneath wliich the 

 fluid is exposed to the influence of the air ; and this is the type 



