M A M M ALIA. 



127 



countries, and we must conclude from the universality 

 of the fact, that there must be something natural in 

 it, the male is, taken upon the average, though there 

 are many individual exceptions, possessed of much 

 more resource than tho female, and we find that the 

 female comes first to maturity. 



But it were idle to follow the details of a subject, 

 the grand connecting portion of which is beyond our 

 reach ; and, therefore, though we cannot but admire 

 the process of growth in animals, and the adaptation 

 of the various parts of that process to the necessities 

 and habits of different animals, yet the commence- 

 ment, the rationale, and the principle of this process 

 lie beyond the reach of our inquiries ; and, whether 

 we address ourselves to the living animal, or dissect 

 and analyse the different parts and structures of the 

 dead one, we equally fail in our attempts to arrive at 

 any thing which we can distinctly consider as life, or 

 the principle of life ; we know life as it displays itself 

 in the living animal, but beyond this we are wholly 

 in the dark concerning it. 



Nor are we better with regard to the particular 

 process by which individual portions of this work of 

 animali.sation is carried on, whether in the growth of 

 the animal body or in its repair. This is the second 

 branch of the general doctrine of organisation ; and 

 the common name of secretion which it has received 

 is of itself enough to show that we know very little 

 about it. There is no doubt that the organic changes 

 constantly going on in the animal body are exceed- 

 ingly numerous ; and that though we give the name 

 of secretions to a certain number of the permanent 

 products of those changes, yet there are others of so 

 evanescent a nature as that they leave no trace in the 

 structure of the animal, but vanish with the action of 

 which they appear to form part. So far all the named 

 secretions, or rather perhaps the preparations for 

 them, appear to be mechanical, and whether the mat- 

 ter of the secretion is taken directly from the general 

 mass of the blood, or consists of other matters, the 

 process is to some extent mechanical. As the se- 

 creting apparatus is approached, there is a subdivision 

 of the conducting vessels into parts still more and 

 more minute ; and it has been found that if a more 

 dense and a more subtle fluid be injected into those 

 vessels by mechanical force, the subtle one will ex- 

 tend further, and into more minute ramifications, than 

 the other ; but in no instance has the seat of secre- 

 tion itself, that in which a distinctly new substance is 

 produced, been reached by any effort of human inge- 

 nuity. This matter of secretion in the body of an 

 animal, whatever the product of the secretory process 

 may be, brings us always to a difficulty of the same 

 kind as the original production of animal matter, and 

 we have no more means of solving the difficulty in 

 the one fuse than in the other. We can follow both 

 to the extreme limit of the eye and the microscope, 

 but at tliis limit they take farewell of us, and veil 

 themselves in obscurity without vanishing from ex- 

 istence. We know that the ramification of the con- 

 ducting vessels into diameters still smaller and smaller 

 at every branch, must mechanically subdivide the 

 blood or other fluid contained in them into parts still 

 more and more minute, as the ramifications are further 

 and further carried on ; and we are also led to sup- 

 pose that in proportion as this division becomes more 

 minute, the action between the internal surfaces ot 

 the containing vessels and the fluids which they con- 

 tain must be greatly increased, upon the principle 



that the contents of vessels are as the square roots of 

 their surfaces, or the surfaces or the squares of the 

 contents. We have also some reason to believe that 

 all living action, whether animal or vegetable, is ulti- 

 mately reducible to the action of surfaces upon each 

 other; for this is really the law which is followed in 

 all the analogous kinds of action, and we find it in 

 every rudimental case in which we can observe action 

 either in animals or in vegetables. All this, however, 

 is but little ; and when we have reached this length, 

 we leave the rationale of secretion as we are forced 

 to do that of life and growth very nearly where we 

 found it. We must, therefore, however desirable it 

 might be to obtain more intimate knowledge of the 

 subject, leave it and proceed to the others. 



Muscular contraction is the one which naturally 

 follows next in order ; and it it is probable that in 

 the growth of animals, it. to some extent or other, 

 is the first modification of what we call the general 

 organising, or rudimental production of an animal. So 

 far as is known, this function is peculiar to animal 

 matter, most ordinarily resident in the muscles, but 

 still transmissible from one part of the body to another, 

 even though there is no muscular connexion between 

 them. This function, or rather the power which is 

 understood to give origin to this function, has been 

 called irritability, and a variety of other names ; but 

 it is like all the other powers for specific purposes 

 which have been attributed to animal bodies, or to 

 different parts of them we know nothing of it as a 

 power, we merely observe certain effects ; and we use 

 this name power, or any of the particular names, for 

 the purpose of enabling us to speak about their un- 

 known causes, by which again is meant those states 

 of the animal body, which take place before we can 

 begin our observation of it, and which of we of course 

 can with certainty know nothing. It was long con- 

 founded with what is called nervous action ; though 

 subsequent experience has shown that though com- 

 bined in producing certain joint effects, they are yet 

 distinct and separate, both in their nature, and in the 

 parts or structures of this animal body in which they 

 peculiarly reside. 



It is of little consequence what name we give to 

 this power, so that we understand the effects of the 

 power itself; but it is of the utmost consequence that 

 we should understand these, and how they differ from 

 each other in different animals, and under different 

 kinds of excitement ; because this is a part of the sub- 

 ject essential to the proper explaining of very much 

 of the action of animals. Haller was the first who 

 gave even a tolerable account of the phenomena of 

 this power ; and as he used irritability as the discri- 

 minating name for it, it is not worth while to alter thy 

 name, if we rightly understand the sense in which it 

 is used. It is not irritability in the common sense of 

 the term, in which it means anything indiscriminately 

 which gives pain or annoyance, which must be under- 

 stood of this irritability of the muscles; it is the fact 

 of a healthy muscle shortening in length, and at the 

 same time swelling out in thickness, when certain 

 stimuli are applied to it. 



What those stimuli are, and whether they are the 

 same, in all natural cases, in the same muscles of the 

 same animal, we have no means of ascertaining ; and 

 there is as much difference among physiologists re- 

 specting the ultimate structure of muscles. They 

 are all composed of fibres as already stated ; but how 

 i those fibres contract is a point upon which there exists 



