These formic acid poisoning references were located by W.C. Monte after publishing his 2011 book.

There was no hemorrhage, edema or any other brain or retinal damage reported in the formic acid deaths.  The deaths show extensive acid tissue erosion with related dysfunctions.


The minimum lethal dose of formic acid is in the range of 65-100 mL (15-20tsp) or 250-375 mg/kg.  
This is about 1/8 the potency of methanol with MLD more like 8.5 mL (1.7tsp) or 90 mg/kg.  

With formic acid, patients come to the hospital about two hours after taking the poison and often succumb soon thereafter.
With methanol there are no symptoms for 18-24 hours and death is also delayed to a few days.

Both poisons cause acidosis, though with formic acid less penetrating of the central nervous system.  In Dalus2013, means for 195 survivors versus 107 non-survivors were:
     formic acid consumed:  73 +-44 mL  versus   181 +-78 mL
                       pH:  7.2 +-0.1   versus   7.3 +-0.1
Normal pH is 7.4 +-0.05
In the methanol poisoning of Appendix A, Charles Fleming was profoundly acidic when he reached the hospital with a CO2 of 7.

With formic acid poisoning, death is 100% if there is perforation of the esophagus, larynx or colon or if shock takes hold.  Conditions significantly correlating with death include purity and quantity of formic acid consumed, abnormally low blood pressure, respiratory distress, severeity of burns, vomiting of blood and metabolic acidosis.  Half of survivors have long term esophageal constriction correlating with blood in stool.

In Dalus2013, the frequency of symptoms among the 107 non-survivors was (from Table 2):  
     acidosis 97%, 
     severe infection 79%, 
     acute respiratory distress 72%, 
     shock 68%, 
     acute kidney failure 54%, 
     aspiration pneumonia 49%, 
     gastrointestinal perforation 36%, 
     excessive pulmonary fluid 25%, 
     esophageal shrinkage 21%, 
     destruction of skeletal and heart muscle 20%.

By organ or system, the effects of formic acid poisoning are:
     Metabolic acidosis:  less severe and less penetrating of CNS than with methanol poisoning
     Kidneys:  blood in urine, then renal failure with biopsy showing death of most tubular cells
     Cardiovascular:  Arrhythmias, profound vascular low blood pressure
     Respiratory:  aveolar inflammation, breathing difficulty, bluish skin from lack of 
             oxygen, lung infection and failure
     Gastrointestinal:  burns, ulcerations, shrinking and hardening of tissue, perforation
     Skeletal muscle loss

*MLD according to Dalus2013 and Rajan1985.  Jefferys1980 MLD is about half as much, 45-60 g (22-50 mL or 5-10tsp).


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Dalus2013:
Dae Dalus, Ashish J. Mathew, and Saran S. Pilai, "Formic acid poisoning in a tertiary care center in South India: a 2-yer retrospective analysis of clinical profile and predictors of mortality," The Journal of Emergency Medicine, 44(2), 373-380, 2013. [302 cases analyzed]

Rajan1985:
N Rajan, R Rahim and S.K. Kumar, "Formic acid poisoning with suicidal intent: a report of 53 cases," Postgraduate Medical Journal 61, 35-36, 1985

Jefferys1980:
D.B. Jefferys, H.W. Wiseman, "Formic acid poisoning," Postgraduate Medical Journal 56, 761-762, Nov 1980

Balagué2014:
Nicolas Balagué, Philippe Vostrel, Jean-Yves Beaulieu and Jan van Aaken, "Third degree formic acid chemical burn in the treatment of a hand wart: a case report and review of the literature," SpringerPlus, 3(408), 2014