071 the Blood cmd Animal Tissues. 137 



ing the fibrillse. In some instances they seem to be continued 

 nearly or quite at right angles completely across the fibril; but 

 frequently the strias in one part are opposite to the spaces in 

 another, by which arrangement a sort of reticulated appearance 

 is produced. The striae are not in all specimens equally distant, 

 but this may perhaps be owing to the elongation or contrac- 

 tion of the fibre. We have discovered this peculiar and very 

 beautiful appearance in the muscles of all animals which we 

 have as yet examined; and as we have seen it in no other tissue, 

 we have been induced to view it as a distinguishing feature of 

 muscle. 



Nerves. — These appear to be essentially composed of fibres, 

 but their structure is looser than that of muscle. Though the 

 fibi'es of nerves do not form such intricate plexuses as those of 

 some other tissues, their coui'se is by no means straight. We 

 have looked in vain for globules, as well as for any trace of 

 medullary matter, which has been somewhat gratuitously sup- 

 posed to be inclosed in the nerves. 



Arteries. — The middle coat of these vessels being still re- 

 garded by some persons as muscular, we were desirous of dis- 

 covering whether its minute structure was at all more favour- 

 able' to such an opinion than its chemical composition. Its 

 subdivision may be carried as far as that of any tissue ; and it 

 evidently consists essentially of long, straight, very delicate and 

 even fibres, which offer no more trace of those transverse strise, 

 which we have regarded as the peculiar characteristic of muscle, 

 than they do of elementary globules. 



The inner coat, when completely detached from other struc- 

 tures, and presenting the appearance of a very thin uniform 

 and almost transparent membrane, is also, by the aid of the 

 microscojje, seen to be composed of fibres, which are extremely 

 delicate, smoodi and uniform, but very tortuous and matted to- 

 gether, in the form of an intricate plexus. 



Cellular Membrane. — This also appears to be very much if 

 not wholly composed of fibres. Our observations respecting 

 this tissue are not as yet complete. 



Brain. — If tliere is any organized animal substance which 

 seems more likely than another to consist of globular particles, 

 it is undoubtedly that of the brain. Our examination of it has 

 as yet been but slight ; but we have noticed that when a })ortion 

 of it, however fresh, is sufficiently extended to allow of its being 

 viewed in the microscope, one sees instead of globules a nml- 

 titude of very small particles, whicii are most irregular in shape 

 and size, and are probably more dependent on the disinte- 

 gration than on the organization of the substance. 



AVwSm>5. Vol.2. No. 8. //;/^. 1827. T The 



