344 CRYSTALLINE LENS. 



matter soluble in water 1.3, insoluble membranous matter 

 2.4. The lens is stated to contain both gelatine and albu- 

 men, but no traces of fibrin have been detected. By burn- 

 ing it to ashes, traces of iron are found. 



The structure of the lens is not satisfactorily settled. All 

 are agreed that it consists of concentric layers, which are 

 easily demonstrated and rendered very distinct by boiling 

 or immersion in a dilute acid. In this manner the layers 

 are seen to be placed one above the other, like the sev- 

 eral strata of an onion, and increasing in density as they 

 approach the centre. These lamina seem to be composed 

 of fibres, extremely thin, and under the microscope present 

 a series of fine teeth united together and interlocking with 

 each other. The lens separates readily into three or four 

 triangular fragments, having their bases at the circumfer- 

 ence, and their apices at the centre. It is surrounded by 

 a membrane called the capsule of the lens. This capsule is 

 elastic, dense, and very transparent, and like the posterior 

 layer of the cornea, boiling and immersion in alcohol do 

 not render it opaque like the lens, and when separated, 

 after being subjected to this operation, its transparency is 

 found to be still preserved. 



The use of this capsule seems evidently designed to pre- 

 serve the form of the lens. , It is described as containing a 

 small quantity of fluid, called the liquor-morgagni, which 

 by some is thought to be rather the result of a cadaveric 

 change. Around the circumference of the lens there is 

 seen a triangular canal called the canal of Petit, which is 

 believed to be formed by the splitting of the lamina of the 

 hyaloid membrane at the lens, one layer going in front of 

 the lens, the other behind, and leaving between the points 

 of separation the above triangular canal. Both the lens 



medium to the many already described as traversed by light. It is very inter- 

 esting to observe, moreover, that nature has not confined herself to an anatomi- 

 cal arrangement in order to obtain a perfect chromatic instrument, but has 

 also resorted, in this instance, to purely physical methods. She has greatly 

 increased the density of this solution towards the centre of the lens, and has 

 accomplished this by a very gradual change, so that this one fluid presents of 

 itself a variety of media for the light to traverse. 



