Having followed this discussion over the last few days, I decided to dig a bit. Our daughter (brief pause for parental pride moment) now in her second year of medical residency at the U of GA, Medical College of Georgia in Augusta..one of the oldest in the South, establish ca. 1824--which might help make it a good source for 19th century medicine research), apparently inherited a bit of her father's "history gene"...but thankfully, her mother's looks and brains!... So, I asked her "medical opinion" of just what "brain congestion" might be defined as in terms of mid-19th century medicine. Here's her response, quoted in part:
"Interesting question, and one that seems to have more than one answer. My guess is it's a catch-all phrase, however, in one specific case (cause of death of none other than Rober E. Lee) congestion of the brain seems to refer to what's now known as ischemic stroke. The mechanism of injury goes like this: a person who usually also has untreated high cholestorol will build up atherosclerotic plaques in the carotid arteries that feed the brain. A piece of plaque breaks off, travels up to the brain via the carotid arery, enters one of the branches and continues into the smaller branches until it eventually lodges, thereby blocking bloodflow in the distribution of that particular artery and its branches. The part of the brain downstream of those branches dies due to lack of oxygen. 140 years later, this is still a major cause of death in the southern US. In Lee's case, the frontal lobes of the brain were affected, which explained his altered behavior at the end without ensuing paralysis, because the frontal lobes control behavior/cognition and not movement or sensation.
"That being said, brain congestion also appears to be related to effects of trauma or infection, and the ensuing cerebral edema (swelling of the brain). The pressure from the swelling also effectively cuts off arterial flow to certain parts of the brain. Same type of ischemic injury, different mechanism, so technically the term "brain congestion" applies. Falls from horses, shots to the head, concussion from explosions, infection (i.e. meningitis or smallpox)--all of those fit the picture and I expect were pretty common causes of death to foot soldiers and mounted officer, alike.
"Hope that helps. I would love to get my hands on some 19th century medical texts. I have a complete set of "Operative Theraputics" circa 1919 that I picked up in an antiques store...a few years ago and a really interesting infectious disease textbook used by the Army in pre-WWII, pre-antibiotic era, but that's about the extent so far. If you have any contacts in your Civil War online groups, I'm willing to negotiate!"
So, that's "the doctor's opinion" on 'brain congestion'...which is, of course, open to a 'second opinion'...and which still leaves open an exact cause of Pvt Daniel's death...was it disease? Head injury? And, if anyone might have a lead on available medical texts of the WBTS era, I'll pass them on to Dr. Jacqueline M. DuBose, MD for her to "negotiate."