160 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



Mr. Toynbee, the posterior half only of the capsule has vessels distributed 

 over it surface ; and these are derived from the Arteria centralis retinae. 

 From optical experiments which have been suggested to him by this circum- 

 stance, he infers that "objects (radiating lines for instance), situated on the 

 anterior surface of the crystalline lens, produce an indistinctness in the image 

 which is formed upon the retina ; whereas, when these lines exist upon the 

 posterior surface of the lens, the image is clear." The substance of the Lens 

 contains about 42 per cent, of animal matter, with 58 parts of water. Nearly 

 the whole of the former may be dissolved in cold water by trituration ; the 

 solution is coagulated by heat, and forms a granular but not coherent mass; 

 alcohol and acids produce the same effect. Hence it appears that the Lens 

 chiefly consists of albumen in its soluble form ; and this may be supposed 

 to be contained in the cavities of the cells, as it is in those of the vitreous 

 humour. From the latest analyses, it appears that the substance of the lens 

 corresponds most with that modification of albumen, which forms the Glo- 

 buline of the blood ( 147). In the Vitreous humour, we have an example 

 of a very loose form of cellular tissue ; strongly resembling that which con- 

 stitutes the entire structure of Acalephse (Jelly-fish). That the cells com- 

 posing it have no open communication with each other, is evident from the 

 fact that, when the general enveloping membrane is punctured in several 

 places, it is long before the contained fluid entirely drains away. This 

 fluid is analogous to that of the Aqueous humour ; being little else than Wa- 

 ter, holding a small quantity of Albumen and Saline water in solution. From 

 Mr. Toynbee's inquiries it would appear, that the vessels which pass through 

 the Vitreous humour do not send branches into its substance ; but that it is 

 nourished by the vessels, which are minutely distributed upon its general en- 

 velope. The Ciliary processes of the Choroid membrane are almost entirely 

 composed of large, plexiform vessels, closely resembling those of synovial 

 membrane (Fig. 54), which allow a great quantity of blood to circulate through 

 them ; and these have probably an important share in the nutrition of the Vi- 

 treous body. 



191. Cartilage is perfectly insensible ; and neither nerves nor lymphatics 

 can be traced into its substance. Its functions are purely mechanical ; the 

 consolidation of its texture by internal deposit renders it little disposed to 

 change by spontaneous decay ; and it is protected by its toughness and elas- 

 ticity from those injuries, to which softer or more brittle tissues are liable. 

 These very circumstances, however, interfere with the activity of its nutrition. 

 Cells which are choked up with interior deposit do not readily transmit fluid : 

 it is doubtful whether any interstitial change can take place in the interior of 

 a permanent Cartilage (except when it has become vascular by disease, or 

 undergoes ossification), through the whole of life; and there seems ground to 

 believe that, when it has been injured by disease or accident, the loss of sub- 

 stance is not repaired by real cartilaginous tissue. In the process of ulcera- 

 tion of Cartilage (as observed by Mr. J. Goodsir), it appears that the formation 

 of depressions on the surface is due, not so much to any change originating 

 in the substance of the cartilage, as to the eroding action of the cells of the 

 false membrane, which is the product of inflammatory action upon its surface; 

 and it is in lliis false membrane that the new vessels are formed, which dip 

 down into nipple-like prolongations of the membrane, entering corresponding 

 hollows excavated in the cartilage. On the other hand, the softer tissues of 

 the Eye are capable of complete regeneration. Every oculist is aware that 

 a great loss of Vitreous humour may take place without permanent injury; 

 and it has been found that even the Crystalline lens may be completely rege- 

 nerated, after it has been entirely removed by extraction. 



