*Sou?nai.Sy'i'i^ Human Vitreous Rumour. 39 
animals. The crystalline lens is an isolated body in the interior of 
the eye, and is dependent for its nutrition on one or more of the 
media which surround it. In many respects its nutrition resembles 
the same process in the vegetable kingdom. Thus, its structure 
continues cellular throughout the whole of its existence;* it 
possesses no nerves, and therefore its nutrition is beyond the influ- 
ence of the nervous system; the nutrient fluid which its cells 
contain is globuHn,t an albuminous compound which has no ten- 
dency to assume spontaneously a higher grade of organization; 
and lastly, when the structure of the lens is once fully formed, it is 
subject to little change of material. It has long been held that the 
lens derives the greater part of its nutriment through the vitreous 
humour, but the structure of the latter not having been satisfac- 
torily determined, the evidence of this was arrived at by " exclu- 
sion"X When the choroid or vitreous humour is inflamed, the 
products arising therefrom are abundantly found in the neighbour- 
hood of the lens, and the latter also participates in the morbid 
action. If the vitreous humour be disorganized, or a great part of 
it lost by accident through a wound of the tunics of the eyeball, 
without injury of the lens, cataract follows ; while if the lens be 
dislocated from its ligamentary attachment, but still adherent to the 
vitreous body, it generally remains transparent, unless the latter 
be disorganized. The convergence of the anastomosing cellular 
tissue of the humour to the posterior surface of the lens indicates 
an intimate association of the nutrition of the two structures, and 
this is peculiarly borne out by the structure of the humour in birds. 
In that division of the animal kingdom the lens undergoes more 
rapid molecular changes than in any other, and the individuals of 
this class have a special provision existing within the eye for the 
supply of the extra demand which necessarily falls upon the nutri- 
tive processes. This consists of a process of the choroid, called the 
pecten, which passes through an opening in the retina at the bottom 
of the eye, and forward in the substance of the vitreous humour to 
near the posterior surface and external margin of the lens. Filling 
up the link between the tip of the pecten and the lens is the anas- 
tomosing cellular tissue of the humour, which radiates in straight 
lines from the former to the latter, thus establishing a communica- 
tion between the vascular choroid and the lens, and which it will 
scarcely be doubted conveys nutriment to the latter. 
These facts point to the vitreous humour as being the principal 
source through which the lens is nourished, thus confirming the 
hypothesis which has all along been entertained ; but the manner 
* Carpenter's ' Human Physiology,' 4tli edition, p, 254. 
t Op. cit., p. 254. 
X The structure of the humour, as now revealed, renders this supposition almost 
a certainty. 
