DIAGNOSIS AND PROGNOSIS. 29 
In attempting to reach a diagnosis it is generally necessary to have the pre- 
vious history. Obviously a knowledge of the duration of the symptoms will 
materially assist in determining whether an existing affection is of acute or 
chronic character. Were a dog recently to all appearances in good health, and 
the attack more or less sudden in its invasion, the disease from which he is suf- 
fering is probably of acute character; whereas, if for a long time he has been 
exhibiting signs of ailing, and the disturbing symptoms are much the same as 
those he has had, only more severe, then nearly all the chances are that his 
affection is chronic and of long standing. 
The reader will doubtless meet cases in which it will not be possible for him 
to make a correct diagnosis. Nor is it reasonable to suppose that in any one 
work on the subjects to which this is devoted, notwithstanding the same be an 
exhaustive treatise, can be embodied all the principles of medicine and teachings 
necessary to make a skilled diagnostician of a layman. Even physicians of the 
highest practical endowments often err in their attempts to discriminate between 
diseases ; and that diagnosis involves more embarrassment than the treatment of 
disease should be appreciated by all. 
A highly effective method of making a diagnosis is called “reasoning by way of 
exclusion.” In a case of doubt the disturbing problem is generally to decide be- 
tween a small number of diseases. From the symptoms noted it is evident that 
the disease to be dealt with is one of two, three, or more, all of which have some 
- resemblance. Now, if it be impossible to determine positively which of those 
diseases is present, it may be practicable to decide that one, two, or more of them 
cannot be the right disease, because certain symptoms are absent. By such pro- 
cess of elimination the number of possible diseases may be reduced even to one. 
The application of this method may be illustrated as follows: — 
A dog does not respond to the usual call, and is sought for in his kennel. He 
is found unable to leave it, and to present these symptoms: His breathing is 
rapid and labored; his manner exceedingly dull; he opens his eyes only to close 
them at once; hangs his head, and it falls as though he slept, but he raises it 
from time to time as he seems to waken or is disturbed by a dry, hacking cough, 
or possibly “gagging,” a result of which now and then is the expulsion of a little 
rust-colored sputa. His nose and body are very hot. He lies down, but soon 
assumes a sitting position, with fore legs quite widely apart and braced. 
The trouble may possibly be in the throat, but it is evidently in the chest. As 
he has been well up to the present time, and the attack was sudden, his disease 
must be acute, therefore all chronic affections may be at once excluded. Mani- 
festly, also, his trouble must be either laryngitis, bronchitis, asthma, pleurisy, or 
pneumonia. 
An examination of the throat dispels the doubt respecting laryngitis. No 
knowledge of a previous attack, and in the absence of wheezing respiration and 
husky, barking cough, asthma is reasonably excluded. In bronchitis, so early-in 
