Phar Lap was a famous race horse in the late 1920s and early 1930s. He won over 70% of the races he entered in four years of racing, due in part to his enlarged heart, which was nearly twice as large as that of a typical horse.
Before he was six years old, he mysteriously died. Various theories as to the cause have been proposed, including poisoning and a bacterial infection.
However, the current data does not conclusively point to one single line of evidence, meaning that none of these theories have been rigorously proven on a scientific basis. Ivan Kempson (Ian Wark Research Institute, Australia) and Dermot Henry (Museum Victoria, Australia) have formally presented chemical evidence that Phar Lap was poisoned with arsenic.
Chemical evidence of arsenic poisoning.
The horse's hide was preserved and has been on display for years. Arsenic was used in this preservation, but as noted further on, this did not prevent a conclusive determination of poisoning.
The scientists removed intact hairs from the hide. They only chose those which had been growing at the time of Phar Lap's death, since ingested arsenic (indicative of poisoning) would leave chemical traces within these hairs.
X-ray fluorescence analysis clearly shows an increase in arsenic at a certain point in the hairs, which by itself is weak evidence of ingestion. More conclusive evidence is that arsenic levels subsequently decrease at the proximal end of the hairs (where the hair is attached to the body), strongly suggesting that the arsenic was metabolised (i.e. not an artifact of preservation).
X-ray absorption near edge spectroscopy and chromatography suggests that the majority of the arsenic in the hairs is in the form of arsenic glutathione, i.e. was biochemically altered (metabolized). This is further evidence that Phar Lap ingested arsenic (was poisoned).
A possible counterargument to the poisoning theory is that horses at the time were regularly given arsenic as a drug. However, the scientists found little evidence of arsenic in the remaining length of Phar Lap's hair, suggesting that he was not regularly given arsenic.
Further investigations.
Phar Lap's autopsy and pre-death symptoms are all suggestive of arsenic poisoning, but these analyses cannot rule out other possible causes of death. This is the first strong chemical evidence of large-quantity arsenic ingestion (poisoning).
This research may lead to investigations on the source of the arsenic. However, it seems unlikely that anyone will figure out exactly who poisoned Phar Lap and for what purpose.
for more information:
Kempson, I. M., & Henry, D. A. (2010). Determination of Arsenic Poisoning and Metabolism in Hair by Synchrotron Radiation: The Case of Phar Lap Angewandte Chemie International Edition, 49 (25), 4237-4240 DOI: 10.1002/anie.200906594