M A M M A L I A. 



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functions which the animal performs ; and then we 

 form our systems, or indices to particular groups and 

 species, upon the modifications of those functions or 

 the results of them. The materials of all this are, 

 however, originally obtained from observations made 

 upon individual animals. 



In the case of a single animal, we naturally say 

 that every thing in the appearance, habit, structure, 

 or any thing else of an animal which we can find in 

 no other department of nature, is the result of a func- 

 tion of animal life ; but this is nothing but a short 

 expression for its belonging: to and being character- 

 istic of an animal, and not of any thing else. 



If we attend duly to such precautions in the use of 

 words as we have now stated, we may with safety 

 introduce a nomenclature, and subdivide and arrange 

 the functions of an animal in the same way as we do 

 the different parts of any other branch of knowledge ; 

 and though the words which we make use of for such 

 a purpose, are nouns or names, as well as those by 

 which we express substantive existences, we need uot 

 on that account confound the realities. 



Animal life, then, is the general name for every 

 function which an animal performs ; and, of course, it 

 varies along with those functions. The principal 

 functions to which it is most essential to advert in a 

 physiological point of view, are organisation, muscular 

 contraction, nervous agency, and sensation ; and upon 

 each of these we shall offer one or two brief remarks. 



Organisation is the name for the general process 

 by which new matter is applied to the body of an 

 animal, whether for the general increase of its bulk 

 by growth, or for the repair of any part that may be 

 \vasted. This organisation is, however, far from a 

 simple result; on the contrary, it is exceedingly com- 

 plicated ; and as we know the function only from the 

 result, the function must be as complicated. The 

 operations which it performs are in brief as follows : 

 first, the original growth of the body ; but this is ex- 

 ceedingly complicated, and is probably very much 

 modified by the other general functions to which we 

 have alluded, and also by the progress of its own 

 development. In the progress of animal growth there 

 is not, in any stage in which we can observe its 

 operation, a mere accumulation of matter upon the 

 rudimental part or germ previously existing. The 

 very matter itself is always a product, and undergoes 

 an operation by which its former aggregation, state, 

 and composition, appear to be completely changed, and 

 a sub-division of all the parts made, probably down 

 to the ultimate atom, before the new compound is 

 formed. This is what we may consider as the initial 

 step of animal organisation, or perhaps we ought to 

 say animalisation, because we must suppose it to take 

 place previous to the formation of any specific organ. 

 We do not, however, find the new matter in the ani- 

 mal structure in that state of its growth which alto- 

 gether precedes organisation ; and therefore the mode 

 of working in this, the most elementary process, must 

 remain one of those mysteries of nature into which 

 we cannot penetrate ; and we know not whether the 

 new matter remains in this first animal state during 

 a measurable portion of time, or during an indivisible 

 moment only. 



The second stage of the process, though still veiled 

 in great obscurity, leaves traces of its operation in 

 the animal ; and therefore, though the working be 

 just as mysterious as formerly, we can see the effects. 

 In the case of the mammalia, we have reason to be- 



lieve that, up to the complete organisation of the 

 young one in the maternal uterus of the placenta I 

 animal, the arterial blood of the mother is the matter 

 which goes to the increase of the foetus ; but even 

 here there is a mysterious application of two surfaces, 

 both apparently imperforate, where the maternal and 

 fetal parts of the placenta are applied to each other, 

 and while we lose the extremities of the maternal 

 vessels as we approach this singular application of 

 surfaces, which appears to perform the functions of 

 union and separation at one and the same time, we 

 are led to conclude that there is a perfect elemental 

 change in this blood before it passes from the one to 

 the other; and we have a further confirmation of this 

 in the fact that the globules of fetal blood are not of 

 the same size as those of the blood of full-grown 

 animals of exactly the same species. 



In the case of marsupial mammalia, we cannot 

 speak with the same precision as in that of the typical 

 or placental mammalia. In them the uterine gesta- 

 tion is no doubt placental, as well as in the others ; 

 though as a placenta, like every other organ, is de- 

 veloped only as it is wanted, it is much more obscure 

 in them. But still when the foetus is transferred to 

 the marsnpium, and freely exposed to the action o 

 the atmosphere, it is still in a very formless and 

 rudimental state, and its future growth, exposed to 

 the action of the air, must be different from that of a 

 fcetus not so exposed. 



In both cases, however, the first development of 

 which we are sensible, is a development of organs ; 

 and it is well worthy of remark, that those organs 

 appear to be developed very much in the ratio in 

 which they are wanted in the economy of the animal. 

 The theory of development formerly alluded to has 

 been had recourse to in this matter, but with very 

 little effect. It does not appear that there is any 

 good ground for supposing that a single organ of the 

 mammalia changes from its original type, with which 

 it starts even before we can observe it ; there is not 

 much greater reason to believe that any one organ 

 originates another, or even that any of the four classes, 

 into which we have said the animal functions can be 

 divided, can in any one of its modifications originate 

 another, although there is not the least doubt that, in 

 their healthiness, and also in their disease, they act 

 and react on each other ; so that though no one of those 

 systematic divisions (for they are not natural ones) 

 can be supposed to originate or give life to another, 

 we have every reason to conclude that the morbidity 

 of any one of them can destroy the soundness of each 

 and all of the rest. We have a proof of this in the 

 application of putrid animal matter, and more espe- 

 cially if it be matter of the body of an animal of the 

 same species, to parts which are sound and healthy. 

 The touch of the sound does not heal the diseased, 

 but the touch of the diseased contaminates the sound, 

 and, whether the corrupt matter is general or local, 

 the portion over which corruption triumphs is lost for 

 ever. The pit of the small pox, or the honey-combed 

 scar left by vaccination, when it takes proper effect, 

 is never obliterated in after-life ; though much more 

 serious injuries, resulting from mechanical means, arc 

 often so changed that hardly a trace of them remains. 



These facts tell us little, however, except the extent 

 of our own ignorance upon this subject ; and the most 

 careful observations, and the most cautious conjec- 

 tures, which have been made on the subject, leave it 

 in its original obscurity. The very first movement of 



