MICROSCOPIC VIEW OP 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 fine 

 fibres, 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 tfre 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 

 fiuid shall be included between them, it is found on submitting it 

 to the microscope, in the same manner as has already been described 



105 



