First, it should be noted that he is referred to as both I. E. Nagle and J. E. Nagle (but it's obvious both are the same person).

According to the History of Hardin County, Ohio, "Dr. Nagle was a Pennsylvanian, who came to Kenton, about 1853. He clerked in a drug store, and, though a physician, never practiced in this locality."
"At the annual meeting [of the Pioneers Systems of Medical Practice of Hardin Co.], held July 9, 1853. Drs. J. F. Perkey, I. E. Nagle, Solomon Kraner, Horace Lawrence and J. A. Rogers were admitted as members."

It was during the Civil War eight years later that Nagle made his big impression.

Some quotes from the book, "Faggots from the Camp Fire" by "a Newspaperman"  (Louis J. DuPre), 1881

page 139
The Alabama poet and literateur [and friend and oft-time opponent of Paul Morphy], Alexander B. Meek, in his book entitled, 'Romantic Passages in Southwestern History,' published in 1837, says that De Soto passed very near the site of the present  beautiful city of Macon. But Judge Meek never heard of Governor Gilmer's carnelian dagger handle or of the discovery more recently made at Macon, in this State.

"When the place was partially fortified not many months ago, Dr. I. E. Nagle, now of New  Orleans, was sent thither to organize army hospitals and provide for the sick and wounded. He was watching Confederate soldiers employed in perfecting old military earthworks planned and upheaved  by prehistoric races in the suburbs of Macon. These earthworks were made after the models used in our time and it was only necessary to repair them. They may have been planned and built by De Soto, but it is much more probable that he, as did these Confederate soldiers, used here, as the latter did the mounds to resist Grant's gunboats along Yazoo Pass, these old strongholds of primeval occupants of the country. In any event, while the Confederates were digging away the base of a broad, earthen wall, they came upon a grave, its occupants' skeletons encased in rust-eaten coats of mail. Dr. Nagle sought to secure the relics, but these were claimed and retained by the owner of the spot, and the doctor was only suffered to have a broken rosary twined about a skeleton's neck. This rosary adorns to-day, so Dr. N. tells me, the walls of the priest's rooms attached to the cathedral in Memphis, Tennessee. A part of the sword of an armored knight remained undestroyed by time; but the armor itself was only a series of layers of iron rust. But full details of this discovery may be obtained by the curious in such matters by addressing Dr. I. E. Nagle, No. 13 St. Charles Street, New Orleans, Louisiana.

this vignette

Page 172
CHAPTER XXV.
Newspaper Life. - Journalism under Difficulties. - A Journalistic Repast. - Jamaica Rum.

"I am sure that people in future years and centuries will be amazed by accounts of our present modes of living. We journalists," said the editor, "have been reduced to the utmost straits. I printed two issues of my Register on pretty wall-paper, using only one side of each sheet. It happened, possibly, because the Confederate Government was getting out a new issue of notes and bonds and monopolized the service of the paper-mills. My only resource was wall-paper owned by a cheerful Hebrew, and the reading matter of the striped sheets was confined to one side of each. It was a queer show when the people, having supplied themselves with accounts of the latest battle, sat along the curbstones and in their doorways holding up the ugly striped, red, white, blue, black, and figured sheets before their eager faces. I was employed, when its editor, John B. Dumble, an Ohio Democrat, was sick, to conduct, for a short time, a daily paper in Atlanta. Sam C. Reid and Dr. I. E. Nagle, two army correspondents of my own newspaper, were in Atlanta at the time. It happened that a blockade-runner had entered Wilmington and supplied us abundantly with Jamaica rum. I paid eighty dollars a gallon and was not aware of the fact that each newspaper of the place, and there were four dalies then published in Atlanta, was in like manner conciliated by the generous importer. There was a famous restaurateur in Atlanta. He drew his supplies of early vegetables and fruits from Florida and commonly spread, though he paid forty cents per pound for salt, a very attractive table. He had no wine, and only the white country whiskey of the period. I discovered my opportunity in the possession of the Jamaica rum, and therefore ordered dinner for eight newspaper men. What was my astonisment when I went to dinner, that I encountered no members of the 'press-gang' except Ried and Nagle. The absentees did not even deign to send apologies for the non-acceptance of my invitation. Nagle and Reid had each seen, during the morning, two of the noble profession, and we inferred, from the condition of these two, that all the rest, as fortunate as I had been, had received a gallon, or even more, of the delicious product of Jamaician distilleries. We three sat down to drink the rum and dispatch the viands before us.

"It was finally proposed and agreed that each of us, and each absent journalist, should contribute a 'rousing dinner-table speech to the delights of the rum occasion.' We sat to work, and each furnished, within three or four hours, two columns of matter for my friend's and my own newspaper. We wrote and published our own and supposed speeches, as genuine, of all the invited editors. We made the ancient and venerated McClanahan pronounce a heartfelt eulogium upon Andrew Jackson Democracy. We reproduced, as Watterson's harangue, the substance of his unique and inimitable delineation of Parson Brownlow's character. It was believed that the parson had died a few days before. Dumble's incisive logic characterized his dinner-table talk. Dill was made to utter a few sentences laudatory of the women of the time, and the whole of these speeches appeared next
morning. Readers of the Appeal and of the Register supposed that the dinner was enjoyed by many guests, and that the speeches were welcomed with loud applause. This was natural enough; but Nagle, Reid, and I were especially dumfounded when we met, three days later, to find that each editor, but one, supposed his published speech genuine; that he had made it as stated, and that his obliviousness of the incidents of the occasion was wholly due to the overpowering influence of Jamaica rum. I congratulated McClanahan next morning after the supposed festival, on his eloquent tribute to the rock-ribbed secession Democracy. He looked at me doubtingly. I said:

" 'Mack, you were a little intoxicated, you remember, but you had your wits about you, and your talking tackle was never in better condition.'

"I produced a copy of McClanahan's own paper and pointed out passages in his speech which I especially approved.

"Still wearing a puzzled look, and rubbing his eyes, McClanahan at last concluded that he had been unconsciously 'the orator of the occasion.' When soon afterward congratulated by Nagle, Mack never hesitated a moment, but replied:

" 'Yes, Doctor, I had been taking a little rum, but made a --- --- good speech; didn't I?'

"Congressmen print speeches, written but never delivered, and distribute them among their
innocent constituencies, and Congressmen have speeches written for them that are delivered as their
own; but here we see that editors not only have speeches written, but delivered  and printed as their own, of which they never heard or dreamed. But the editors deserved the more  praise and less censure in this, that each honestly supposed he made the speech ascribed to him, and each earnestly congratulated the other because of his triumph, and the innocent people were not sought by the journalists to be humbugged."

according to one site holding some personal papers:

"In July, 1861, Nagle offered his services to the Arkansas State Militia, and was ordered to proceed to the hospital at Pocahontas. On July 31, William J. Hardee appointed Nagle assistant surgeon in the Confederate States Army, and placed him in command of the hospital at Pocahontas."
Major (then Brigadier) Gen. William Joseph Hardee wrote to "Nagle to express his pleasure at the skill with which the doctor had organized the hospital at Pocahontas."
Nagle worked as a surgeon for the 6th Kentucky Cavalry, the 1st Division, the 33rd Alabama
Volunteers and others. Besides Pocahontas, he served at Gilmer Hospital in Chattanooga and oversaw the hospital at Graysville, Georgia. He is known to have been at the battle of Frederickstown  on Oct. 21, 1861; probably served in the defense of Atlanta and definitely at The Battle of Missionary Ridge.

In May 1879 St. Nicholas Magazine published Nagle's story, The Big Bear of Wannetola (A True Story).
The new annals of the Civil War,  edited by Peter Cozzens and Robert I. Girardi 2004 contains I. E. Nagle's account of The Battle of Missionary Ridge.