3 22 TUBERCULAR DIATHESIS : ITS TREATMENT. 
cold and damp, long-continued mental depression, &c. The 
treatment of the Tubercular diathesis (as this state of consti¬ 
tution is termed) must be directed to the invigoration of the 
system by good food, active exercise, pure air, warm clothing, 
and cheerful occupation; and by the due employment of 
these means, at a sufficiently early period, many valuable lives 
may be saved which would have otherwise fallen a sacrifice. 
The value of cod-liver oil in the treatment of this disease, 
which is now a well-established fact, seems to depend upon 
the facility with which it is assimilated as a nutritive material. 
It is a remarkable fact that the inhabitants of Iceland, the 
greater part of whom live under conditions that might be 
expected to favour the development of tubercular disease, are 
singularly free from it; and the source of this exemption 
seems to consist in the very oleaginous nature of their diet. 
Consumption presents itself among the inhabitants of all 
climates; and the value of change to a patient who is 
affected with this malady, chiefly depends upon the oppor¬ 
tunity which it affords him for abundant exercise in the open 
air, without injurious exposure to cold or damp. 
387. From the foregoing facts it is evident, that the opera¬ 
tions of Nutrition are due, on the one hand, to the indepen¬ 
dent properties of the several Tissues, which draw from the 
blood the materials of their continued growth and renewal; 
and, on the other, to the properties of the Blood, which 
supplies them with these materials. The blood, left to itself, 
could form no tissue more complex than a mere fibrous net¬ 
work : whilst, conversely, the various tissues of the body 
could not draw their nourishment directly from the products 
of digestion, and are consequently dependent upon the blood 
for their supply. We may illustrate the relation between the 
three states,—that of aliment, blood, and organized tissue,— 
by comparing them with the three principal states which 
Cotton passes through in the progress of its manufacture,— 
namely, the raw cotton, spun-yarn, and woven fabric. The 
spun-yarn could not of itself assume that particular arrange¬ 
ment which is given to it by the loom; and the loom could 
make nothing of the raw cotton, until it has been spun into 
yarn. 
388. It is also evident, that the blood-vessels have no other 
purpose in the act of Nutrition, than to convey the circulating 
