300 NATURE AND LIFE. 
the science of life and diseases. This is a mine in which 
priceless and unexplored veins are yet abundant. Great 
triumphs are in store for those who shall have skill to ex- 
tract that metal and bring it into circulation; but such labor 
demands bold enterprise no less than sagacious diligence. 
There are diseases which have their seat in some one 
of the viscera, and at first oppress it alone with suffering. 
Thus the lungs, the liver, the stomach, the brain, may be 
differently affected. Others extend to a whole organic sys- 
tem, as the nervous or muscular system, that of the joints 
or the skin, ete. Others, again, seize on the whole vital 
frame, and to these is given the name of general disorders. 
It is as to these that we have least acquaintance with the 
outward causes and the internal derangements, because 
both have hitherto remained beyond the reach of medical 
research. Yet we may affirm that the blood, which bathes 
the whole organism and maintains the connection between 
the parts in it, must be in such cases the chief seat of mor- 
bid change. Without here going into the details of the dis- 
tinctions set up by pathologists between disorders of this 
nature, it will suffice to say that they have classed cholera 
among the infectious diseases, that is, among diseases oc- 
casioned by poisons that have their origin in the atmos- 
phere, as the yellow fever, the plague, typhus, varioloid, 
typhoid fever, etc. 
Whatever hypothesis we may form as to the atmos- 
pheric origin of which we have just spoken, it is clear that 
these diseases affect the blood. In them the nourishing 
fluid experiences a transformation, not merely in the order 
and proportion, but also in the nature, of its components, 
particularly the most important of all, the albuminoid mat- 
ter. The latter, which is the essential and nutritive part 
of the blood, the plastic part, to which the exhausted tis- 
sues owe their body and spring, then undergoes a deep 
change in the inmost parts of its molecular composition. 
