FUNDAMENTAL PRINCIPLES OF DISEASE. 389 
blood vessels, and is distributed to distal parts. Essential fevers are 
those in which there is from the outset a general disturbance of the 
whole economy. This may consist of an elementary alteration in the | 
blood or a general change in the constitution of the tissues. Fevers 
of the latter class are usually due to some infecting agent and belong, 
therefore, to the class of infectious diseases. 
Essential fevers are subdivided into ephemeral fevers, which last 
but a short time and terminate by critical phenomena; intermittent 
fevers, in which there are alterations of exacerbations of the febrile 
symptoms and remissions, in which the body returns to its normal 
condition or sometimes to a depressed condition, in which the func- 
tions of life are but badly performed; and continued fevers, which 
include contagious diseases, such as glanders, influenza, etc., the septic 
diseases, such as pyemia, septicemia, etc., and the eruptive fevers, 
such as variola, etc. 
Whether the cause of the fever has been an injury to the tissues, 
such as a severe bruise, a broken bone, an inflamed lung, or excessive 
work, which has surcharged the blood with the waste products of the 
combustion of the tissues, which were destroyed to produce force, or 
the toxins of influenza in the blood, or the presence of irritating ma- 
terial, either in the form of living organisms or. of their products, 
as in glanders or tuberculosis—the general train of symptoms are 
much the same, varying as the amount of the irritant differs in 
quantity, or when some special quality in them has a specific action 
on one or another tisgue. 
There is in fever at first a relaxation of the small blood vessels, 
which may have been preceded by a contraction of the same if there 
was a chill, and as a consequence there is an acceleration of the cur- 
rent of the blood. There is, then, an elevation of the peripheral 
temperature, followed by a lowering of tension in the arteries and 
an acceleration in the movement of the heart. These conditions may 
be produced by a primary irritation of the nerve centers of the brain 
from the effects of heat, as is seen in thermic fever, or sunstroke, or 
by the entrance into the blood stream of disease-producing organisms 
or their chemical products, as in anthrax, rinderpest, influenza, etc. 
There are times when it is difficult to distinguish between the exist- 
ence of fever as a disease and a temporary feverish condition which 
is the result of excessive work. Like the condition of congestion of 
the lungs, which is normal up to a certain degree in the lungs of a 
race horse after a severe race, and morbid when it produces more than 
temporary phenomena or when it causes distinct lesions, the tem- 
perature may rise from physiological causes as much as four degrees, 
so fever, or, as it is better termed, a feverish condition, may follow 
any work or other employment of energy in which excessive tissue 
