MICROSCOPIC VIEW OF MILK. 
cork, the blood can be traced in its course to the extreme arteries, 
and thence from the smaller to the larger veins on its return to 
the heart. 
84. The vascular system of the tongue appears traced upon a 
greyish semi-transparent brown, on which a multitude of line 
libres, v v, are seen extended in different directions ; these 
existing at different depths within the thickness of the tongue, 
appear superposed and interlaced; these fibres belong to the 
muscle of the organ, and their characteristic action is rendered 
evident in the microscope, by their alternate contraction and 
extension. A number of greyish spots, somewhat round in their 
outline and a little more opaque than the neighbouring parts, 
appear scattered through the tongue; these spots belong to the 
mucous-membrane, and are in fact parts of the glands in which 
saliva is secreted. They are the theatres of a surprisingly 
complicated and active blood-motion. The sanguine fluid enters 
them at one side, generally by a single small artery, rarely by 
two, and following the course of this artery, it pursues a nodu¬ 
lated path, resembling the form of a bow of ribbon, or the 
figure 8, and issues from them at a point opposite to that it entered. 
The organ of which we speak, says Dr. Donne, having a certain 
thickness, we cannot always see at once the entrance and departure 
of the blood, the point of its departure being often in a plane 
inferior or superior to that of its entrance, and the two points 
not being, therefore, at the same time in focus. But in any case, 
nothing can be more curious or more profoundly interesting than 
the vortices of rapid circulation, thus exhibited, in a space so 
circumscribed and within the limits of an organ, which is evidently 
one of secretion. 
85. These greyish spots in short, in which the circulation proves 
to be so active, are nothing but the mucous-follicles of the tongue, 
the little glands in which is secreted the viscous humour which 
coats in such abundance the tongue of the frog, and we accord¬ 
ingly find that if it be wiped off', it will be almost immediately 
reproduced. 
86. The milk of mammalia being the first nourishment taken 
by their young, and their only nourishment until a certain epoch 
of their growth, it might naturally be expected that that fluid 
would have a close analogy to the blood. The examination of 
milk accordingly, whether with the microscope or by means of 
chemical analysis, proves such an anticipation to be well-founded. 
If a small drop of milk be laid upon a clean slip of glass, and 
covered by a thin film of glass, so that a thin stratum of the 
fluid shall be included between them, it is found on submitting it 
to the microscope, in the same manner as has already been described 
105 
