This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
In typhoid or "low" fever, hydrochloric acid had, at one time, a high reputation; it was said to moderate the pyrexia, to limit the alteration of the blood, and to directly influence the morbid process. We scarcely expect so much now, but still there is reason to think that a judicious use of this acid may favor the assimilation of food, if it do not exert antiseptic influence. According to the investigation of Manassein, with the gastric juice of fever patients, it is not pepsine that is deficient but acid, and this deficiency may be supplied for a time by the artificial acid, which then much aids the impaired digestion. It matters little whether we say with this observer, and with Chambers, that we supply deficient acid, or, with Richardson, that we neutralize by it super-abundant alkali formed during fever. Chambers records an emphatic opinion as to its value, after a fairly extensive use of it at St. Mary's Hospital, in "low" fever, apparently typhus and typhoid. The treatment by hydrochloric acid was more successful than by any other method, but we must add that he conjoined with the former, strict attention to nourishment, giving milk and beef-tea regularly every two hours, day and night (Medical Times, 1858; Medico Chirurgical Review, ii., 1863). Henderson has reported on its value during an epidemic at Shanghai (Medical Times, i., 1863). On the other hand, Dr. G. Johnson is satisfied with the far better progress made by his typhoid patients in King's College Hospital since he omitted wholly mineral acid from their treatment. He finds, especially, that diarrhoea is less troublesome, and considers that acids irritate the bowels, just as bread or meat would do (British MedicalJournal, i., 1875). I cannot think Dr. Johnson's reasoning very conclusive, though his facts are of course to be accepted. I think the acid sometimes useful, and if well diluted the doses required will not irritate the bowels. It may be given as a refrigerant drink in lemonade, or mixed with essence of meat so as to aid assimilation.