602 



SUPPLEMENT 



the fluids undergo a preparation for (lie pur- 

 poses they are to serve. " The woody-fibre is 

 best observed in the vertical sections, cut either 

 parallel or perpendicula'r to the medullary 

 rays : it consists of slender tubes gradually 

 diminishing towards the ends. The fibres 

 vary greatly in diameter ; the largest are in 

 the coniferae : in the lime-tree they often ex- 

 ceed l-50th of an inch. The vascular tissue 

 consists of membraneous tubes, with conical 

 extremities, internally furnished with fibre. 

 When the fibre consists of one or more threads 

 coiled spirally like a screw, it is called a spiral 

 vessel ; when the fibre consists of rings, it takes 

 the name of annular vessel; and if in small 

 pieces, ducted vessels, either reticulated or dotted." 

 The vascular tissue of plants acts in concert 

 with the cellular tissue for the collection and 

 preparation of the nutritive fluids. Our mi- 

 croscopic knowledge of the economy of vege- 

 table organization, is far from being complete ; 

 and, perhaps, at present we can do little more 

 than express our admiration at the wonderful 

 operations which muslbe continually going for- 

 ward in that laboratory, the trunk or stem of a 

 tree. " Every tree," Adams observes, "may be 

 considered as consisting of numerous concen- 

 tric strata or flakes, forming so many cones, 

 inscribed one within the other, and whose 

 number is almost indefinite. The most ex- 

 terior contain the rudiments of the bark ; the 

 more interior, those of the wood. In the 

 germ they are gelatinous, by degrees they 

 become herbaceous, and in process of time 

 assume the consistence of wood. Thus the 

 stem, the root, and the branch, may be con- 

 sidered as formed of a prodigious number of 

 concentric vertical strata, each composed of 

 different fascicles of fibres ; which fibres are 

 again formed of smaller ones. The spaces 

 between these, and among the fibres, are filled 

 up, interwoven with, and connected by the 

 cellular tissue, of which the radial insertions 

 are formed." 



Plate 35, fig. 39, exhibits the singular 

 formation of the aloe as developed in a trans- 

 verse section, under the amplifying power of 

 100 on the surface. This object discovers the 

 character of cellular tissue in a very pleasing 

 manner. 



Fig. 40, shows the fine longitudinal fibres of 

 the palm, under a superficial power of 90,000. 

 Fig. 49, is a transverse section of the 

 clematis, showing, under a superficial power 

 of 400, the wonderful arrangement and ex- 

 quisite structure of its tissues. 



We come now to consider the minute for- 

 mations and phenomena of the animal kingdom. 

 A large volume would scarcely suffice for a 

 particular and detailed examination of animal 

 minutiae : all therefore, that we can propose 

 to ourselves in a division of a single chapter, 



is to take a general and comprehensive survey, 

 particularizing only in a few instances by way 

 of illustration 



We commence with a slight notice of the 

 bony structures in animals. These are brought 

 under microscopic examination, in the same 

 way as the cuttings of wood ; viz. by obtaining 

 extremely thin vertical and transverse sections, 

 which are to be viewed both in a dry state and 

 moistened with water. We are instantly struck 

 with the resemblance between them and 

 vegetable formations : in the transverse sec- 

 tions we observe the cavity formerly occupied 

 by the marrow, answering to the medulla in 

 plants; the perforations, resembling cellular 

 tissue ; and the concentric circles, indicating 

 the process by which the structure is enlarged. 

 In verticle and oblique sections the vegetable 

 analogy is still preserved, in the disposition 

 and character of the fibres. The muscles of 

 animals are to be examined in like manner ; 

 by cutting thin slices of dried flesh in various 

 directions, and viewing them first in their dry 

 state, and afterwards when saturated with 

 water. The formation of the fibres and 

 muscular vessels, (the latter much resembling 

 the vascular tissue of plants,) is worthy of at- 

 tentive examination ; it is not, however, the 

 mere beauty or singularity of formation that 

 renders them interesting, for from a micro- 

 scopic investigation of these structures we are 

 enabled to infer with certainty concerning the 

 strength and activity of the animals to which 

 they respectively belong. The horns, hoofs, 

 nails, &c. of animals form a class of objects 

 that are brought under view in the same man- 

 ner as the preceding. Thin slices cut in 

 two or three directions exhibit the fibres and 

 cellular cavities ; and a vegetable structure is 

 farther evidenced by treating them as opaque 

 objects, and observing the character of the ex- 

 terior. If, for instance, the outer surface of 

 the human nails be attentively examined, it 

 will be found to consist of a vast number of 

 layers ; and if we fake a hedgehog or porcu- 

 pine's quill (the slructure of which is the same 

 in principle with that of the nails, hoofs, &c.) 

 we shall discover the true nature of these 

 layers, which are, in fact, conical cups shoot- 

 ing successively one out of the other. Plate 

 34, fig. 27, exhibits a transverse section of a 

 hedge-hog's quill, wherein we see a medulla 

 or pith, cellular cavities, and other vegetable 

 characteristics. We perceive, then, a won- 

 derful analogy in these structures to the 

 woody formations of trees, both in the internal 

 disposition of parts, and the exterior accessions 

 arising from progressive growth. The hairs 

 of different animals are very similar to the 

 horns and nails, &c. inasmuch as they consist 

 of cups inserted within each other, and in- 

 teriorly exhibit, (so far as micrographers have 



