ANIMAL. 



135 



that regards their nutrition. The processes that 

 lead to this conclusion may be, and, indeed, 

 are more complicated among animals than 

 among vegetables ; but the essence of the final 

 act is very nearly the same in both. Neither 

 shall we be able to demonstrate any great 

 want of uniformity between these different 

 classes of organized beings in several of the 

 actions which we shall next discuss ; in others, 

 however, we shall discover an impassable line 

 of demarcation between them. The first of 

 these actions which we shall consider is 



Secretion. We have already had occasion 

 to mention the watery exhalation and oxygen 

 thrown oft' by the leaves of vegetables. Divers 

 other substances are excreted by the same parts, 

 water, various acrid, glutinous, saccharine, 

 and balsamic substances. It is even by means 

 of the leaves that vegetables throw out. those 

 substances which they may have absorbed by 

 their roots, and which seemed calculated to 

 injure them. We are at no loss, moreover, to 

 demonstrate numerous apparently glandular 

 organs in vegetables for the elaboration of a 

 variety of substances, many of them very acrid. 

 The flowers of vegetables secrete, in the first 

 place, certain matters, the infinite variety of 

 whose odours proclaims them to be different; 

 the nectaries are also filled with fluids, which 

 are sweet in many tribes. Lastly, in the 

 flowers, the male fecundating matter, and the 

 fluid that moistens the pistillum are secreted. 

 Nor are vegetables without internal secretions, 

 among the number of which certain aeriform 

 fluids are not the least curious. The other 

 secretions of vegetables are of infinite variety, 

 gummy, oleaginous, balsamic, camphoric, 

 &c. &c. These are all stored up in cells con- 

 tained in different parts of each individual 

 plant, and undoubtedly either subserve im- 

 portant purposes in their several economies, 

 with the nature of which we are very imper- 

 fectly acquainted, or are in relation with some 

 other system in the universe, affording food to 

 numerous tribes of insects, or materials which 

 stand in relation to animals and man as means 

 of accomplishing a variety of ends, the impulses 

 to which they bring into the world with them, 

 though they are launched upon existence un- 

 furnished with the materials. 



We have also hinted at the watery and 

 gazeous products of the respiration of animals, 

 and consideration for a moment enables us 

 to make a long catalogue of other secretions 

 both with reference to individuals and to 

 species. We have, for instance, the limpid 

 fluids that bedew the cellular and serous mem- 

 branes, serum and synovia, and fill various 

 cavities in the body the chambers of the 

 ear and of the eye particularly ; those that 

 moisten and defend the surfaces of the mucous 

 membranes, the tears and mucus ; those that 

 are subservient to digestion, the saliva, gastric 

 juice, pancreatic juice, and bile ; those that 

 lubricate and prevent the surfaces exposed to 

 the air from drying, the sebaceous or oleaginous 

 fluids of the skin, and cerumen of the ears ; 

 those that are laid up as reservoirs of nutriment 



or defences from the cold, the fat, marrow, &c.; 

 those that are the vehicles for the worn-out 

 particles of the body, the urine and perspira- 

 tion ; those that minister to the reproduction 

 of the species, the fluids of the female germ 

 or ovum, the spermatic and prostatic fluids 

 of the male ; and finally, those that are poured 

 out among the mammalia as the first aliment 

 for the newly-born being, the milk. Nor is 

 the list exhausted, for numerous species of 

 animals have peculiar fluids which are useful 

 to them in the places they hold in the system 

 of creation ; among these are the venomous 

 fluids of serpents, and of the stings of numerous 

 insects, the inky fluid of the cuttle fish, the 

 fetid fluids of the anal glands of the carnivora, 

 rodentia, &c. ; the fluid with which spiders 

 weave their web ; the wax with which bees 

 build their cells, Sec. Secretion is, therefore, 

 a much more extensive function among animals 

 than among vegetables ; the products are still 

 more various, and the apparatus by which they 

 are eliminated is, generally speaking, far more 

 complicated among the former than among 

 the latter. Certainly, in the very lowest tribes 

 of animals, secretion is an exceedingly simple 

 process contrasted with what it becomes in the 

 higher, whose organization is more complex. 

 Among the polypi, medusae, and entozoa, 

 the whole of this function seems to consist in 

 a kind of transudation, or exhalation from the 

 surface of their homogeneous bodies, without 

 the intermedium of any special organ. Among 

 animals higher in the scale we find secretion 

 performed in two modes, by vessels, when 

 the act is entitled exhalation, and by means 

 of certain special organs named glands, an 

 arrangement which we also find among vege- 

 tables. The skin and pulmonary surface are 

 the great implements of exhalation among 

 animals, as the leaves are among vegetables ; 

 almost all the rest of the secretions take place 

 by the instrumentality of glands. 



In vegetables secretion seems to be limited 

 to the preparation of the nutrient fluid by the 

 elimination of certain matters, and, so far as 

 our knowledge extends of the end to be an- 

 swered by any act, for the formation of the 

 generative fluids; we do not, in fact, find 

 among vegetables any apparatus set apart for 

 the excretion of matters derived from a change 

 in the constituent particles of the organs once 

 formed. Among animals, again, the apparatus 

 by which this depuration of the system is ac- 

 complished is one of the most important of all 

 to the preservation of the individual. Secretion 

 among vegetables is a function much more 

 under the influence of external circumstances 

 than it is among animals ; it is also more sub- 

 ject to periodical changes among the former 

 than among the latter, and whilst the function 

 is mostly called into activity by the stimulus of 

 light, heat, &c. in the one, it rather obeys cer- 

 tain internal and peculiar stimuli transmitted 

 through the medium of the nervous system in 

 the other. 



Like all the other special modes of activity 

 manifested by organized beings, secretion is 



