With respect to the characteristic features of yellow fever, and the different signs, by which it may be distinguished from bilious fever, I must be very brief; as a great deal having been written on the subject, any long details in this place would occasion undue repetition of what is already known to the profession. A few words, however, may not be improper. Every one who has had frequent opportunities of seeing the yellow fever, must have noticed, among its most habitual signs, a peculiar inflamed glassy appearance of the eye, easily recognised, but difficult to describe. It is one, however, on which I should be willing to place considerable reliance, in establishing my diagnosis of this disease; as I do not recollect to have noticed it in any other form of febrile affection. Together with this, there is, in the majority of cases, an intense supra-orbitar pain, apparently unconnected with great disordered action of the brain, as the intellectual functions are generally unimpaired. These two signs, together with pain in the loins, and, in more advanced periods, the peculiar appearance of the skin, the vomiting of the coffee grounds matter, the intermission on the 4th day, the retention of muscular strength, and suppression of urine, are the only signs by which the yellow fever, so far as I am prepared to say, may be recognised. In regard to the supposed identity of this fever with the bilious, a great deal has been written; but I must confess, that I feel inclined to doubt the correctness of this opinion, for the following reasons:
1st. Bilious fever is almost always a remittent fever, presenting regular exacerbations, and, unless arrested by medical aid or some effort of nature, running its course, in a progressive manner, either to a happy or fatal termination; whereas the yellow fever is almost invariably a continued fever, presenting obscure and irregular, or even no remissions. On the fourth day, it generally presents so perfect a remission, as to cause the patient, in many cases, to imagine himself perfectly free from disease, and induce him to get up, and even sometimes to walk out. This remission, which sometimes amounts to an intermission, so far as an experience of upwards of forty years can authorize me to decide, is never found to attend in bilious fever, in which, if there be any remission, and recurrence of the unpleasant symptoms, the former is always a real convalescence, and the latter an accidental relapse.
2nd. The red colour of the eye, to which I have alluded above as occurring in the early stage of the yellow fever, and its peculiar yellow tinge in the after part of the disease, are different from the redness and yellowness of the same organ in bilious fever; in the first stage of which the eye presents a more fiery redness, and in the subsequent period, a more saffron yellowness.
3d. The colour of the skin in the two diseases presents also some difference, being more constantly noticed in yellow fever, and disappearing much more rapidly than in bilious fever. In yellow fever, moreover, it assumes, most commonly, a yellowish-brown or even mahogany tinge; whereas in bilious fever, when it occurs, it does not differ from the ordinary jaundice colour, of a lighter or deeper shade.
4th. These fevers may likewise be distinguished by an attention to the state of the intellectual faculties, and of the muscular strength; these remaining often unimpaired to the last in yellow fever, whereas, in a very large majority of cases of bilious fever, the mind becomes soon involved in the disorder of the system, and the greatest muscular debility prevails, even from the very onset of the attack.
5th. The matter vomited might of itself serve to distinguish the two diseases. Independently of the difference we shall notice when speaking of the black vomit, we may mention that patients complain, even sometimes from the commencement of the attack, of the acidity of the vomited matter; whereas in bilious fever, the mouth is bitter, and the matter ejected of the same taste.
6th. As a further mark of difference, we may state, that, in yellow fever, the tongue, except at the tip, the skin, and the pulse are sometimes little altered; whereas in bilious fever they are usually pretty much so.
7th. In respect to the duration of the two diseases, we may state as a general rule, that yellow fever runs its course to death or convalescence, in a much shorter time than bilious fever. Nor is the promptness of recovery from yellow fever less different from the slowness of convalescence, noticed in most cases of bilious fever.
8th. The suppression of urine is a frequent attendant on the last stage of yellow fever, and is seldom noticed in bilious fever.
9th. I have never witnessed a second attack of yellow fever in the same individual; whilst on the contrary, so far as I have seen, there is no limitation to the number of times a person may be affected with the other form of fever.