184 MR. TOYNBEE ON THE ORGANIZATION AND NUTRITION 



above, extend upon the anterior surface of the capsule. Immediately they reach 

 the latter they become straight, run parallel with each other, and are directed 

 towards the centre of the anterior surface for the distance of a quarter of a line, when 

 they stop in their course, and form looped dilatations, which give origin to small veins, 

 Plate XVI. fig. 6. It is most probable that these vessels recede at subsequent periods 

 of development, so as to leave the whole of the anterior surface of the capsule 

 capable of being permeated by the rays of light*. These vessels, in a diseased state, 

 are sometimes prolonged into the whole of the anterior capsule, (or to speak with 

 more propriety, the anterior half of the capsule,) where, in morbid specimens, they 

 have been injected by Schroeder Van der Kolk. The capsule of the lens is thus 

 pervaded by large and numerous ramifications of blood-vessels, which I believe pour 

 out upon its inner or lenticular surface a nutrient fluid ; this fluid will immediately 

 come in contact with the mass of delicate cells described by Schwann as situated be- 

 tween the lens and the capsule. 



The mode of nutrition of the crystalline lens may be explained, by supposing that 

 the nutrient fluid is received by the cells just alluded to, and conducted to the lens 

 (perhaps has its characters changed in its course by the metabolic functions ascribed to 

 them by M. Schwann) through which it is diff'used. It has been stated, that the pre- 

 sence of blood-vessels in the cornea, the anterior half of the capsule of the crystalline 

 lens, and in the substance of the lens itself, appears to be incompatible with their 

 function of transmitting the rays of light to the retina. Nevertheless large vessels 

 ramify on the posterior half of the capsule. The knowledge of the existence of this 

 arrangement of vessels led me to perform some experiments with lenses, from which 

 I have deduced the fact, 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 ihQ posterior surface 

 of the lens, the image is perfectly clear. 



3. The Vitreous Body or Humour. 



Structure. — The vitreous humour is composed of cellular cavities which are filled 

 with a transparent fluid. The membrane of which the walls of these cells are com- 

 posed, — the tnnic of the vitreous humour, — is very delicate, and is interspersed with 

 corpuscles. 



The Vessels of the Vitreous Humour. 



Many anatomists -f- have stated that the arteria centralis retinae, in its course through 

 the vitreous humour, gives off" minute branches into the substance of the latter ; but 

 these branches have never been described ; on the contrary, Mijller, who has paid 



* I have hitherto not succeeded in making a complete injection of these vessels in the adult subject, 

 t Harrison, Boyer, Cruveilhier, &c. 



