^j!)uralijun%9^^ Suman Vitreous Eumour. 37 
short focus at the flame of a candle two or three yards distant ; * 
but by thus viewing them it would never be suspected that they 
enclose the delicate structure delineated in Fig. 1 (page 376). Be- 
sides age in the dead subject, these globules are also rendered more 
fluid and become detached by the addition of the caustic alkalies, or 
by the application of a moderate heat, disclosing the structure 
which they obscured ; but they are not dissolved or detached by the 
dilute mineral acids. Kespecting the nature of the fluid of which 
these globules are composed, it presents no tendency to pass spon- 
taneously into a state of fibrillation, and therefore it has no claims 
to be ranked with lymph or any of the normal fluids of the body 
which contain fibrin ; and in being quite insoluble in the ordinary 
vitreous fluid, it is at once distinguished from albumen, at least in 
the condition in which that substance is secreted by the ciliary pro- 
cesses. In its behaviour with chemical reagents, and in being with 
dij9S.culty coagulated by heat, it answers to the description of the 
globulin of the blood. But, whatever name be applied to it, there 
can be no doubt that it belongs to the albuminous type of com- 
pounds ; and as the vitreous fluid, when secreted, contains no other 
histogenetic compound than albumen, it seems a safe deduction that 
these beautifully transparent globules consist of albumen in the act 
of undergoing a metamorphosis into a higher state of elaboration. 
As to the office of these globules in the vitreous humour, by forming 
an impervious coating upon the fibres of the anastomosing cellular 
tissue, they protect the latter from maceration in the fluid in which 
it is constantly bathed, and their plastic property will necessarily 
add strength to the fibres. But their prime function is, no doubt, 
the supply of nutriment for the fabric of the humour, or for other 
parts. 
Assuming these globules to be derived in the manner already 
supposed, their formation is dependent on the assimilating power of 
the tissue of the humour, which in that case must be endowed with 
a certain amount of vitality. We have abundant evidence of the 
existence of this force in the humour : in its development in the 
embryo ; in its organization in the adult ; in its undergoing mole- 
cular decay, the products of which have been demonstrated in the 
vitreous fluid by chemical analysis ; in its constant maintenance in 
a state of transparency, though it contains a decomposable struc- 
ture ; and in its undergoing the process of putrefaction after death. 
It would seem, also, as if the globules adhere to the tissue by the 
force of vital attraction ; for they become detached of their own 
accord soon after death. But if any doubts exist as to the presence 
* For the manner in which the structure of the vitreous humour may be viewed 
entoptically, see Mackenzie " On the Vision of Objects on and in the Eye," ' Edin- 
burgh Medical and Surgical Journal,' No. 164; also James Jago, M.D., 'On 
Entoptics,' London, 1864, p. 74. 
