"The Gemsbok (Oryx gazella) is the large antelope of the Kalahari and Namib — striped in black and white across the face and flanks, carrying straight rapier horns that reach one hundred and twenty centimetres and have been documented killing lions. Both sexes carry horns, which is unusual. The animal can raise its body temperature to forty-five degrees Celsius — a level lethal to most mammals — storing heat rather than sweating, to preserve water. The brain is protected from this stored heat by a rete mirabile, a network of fine blood vessels where blood cooled in the nasal passages passes alongside blood travelling to the brain, cooling it selectively. The body stores the heat. The brain stays cool. The animal can survive indefinitely without drinking water. The author spent the afternoon in the same landscape and did not find it comfortable."
He had been watching the gemsbok for forty minutes when he stopped writing and simply watched.
The thermometer on the camp table read forty-one degrees. The gemsbok was grazing at the acacia edge without apparent modification to its programme. It had been doing this when the Colonel arrived and was doing it still — the methodical forward movement, the head down at each clump of dry grass, the occasional pause to scan the horizon with the unhurried competence of something that has assessed this landscape and found it, with all its current temperatures, adequate.
The Colonel was in the shade of the camp awning and was not finding the temperature adequate.
He had written, in the margin of the morning's entry: "Gemsbok grazing. Midday. Temperature: significant. Animal: apparently unconcerned. Investigating."
He investigated.
The rete mirabile occupied the next two pages.
He had the anatomy reference — had been carrying it since Cape Town — and had not opened the gemsbok section because he had not previously had cause. He had cause now. He read the relevant passage and then read it again and then looked at the gemsbok, which was still grazing at forty-one degrees.
The body stores the heat. This was the mechanism — instead of sweating, which uses water, the gemsbok allows its body temperature to rise during the day, storing the heat that other mammals expend water to remove. A body temperature of forty-five degrees is the upper limit at which most mammals survive. The gemsbok reaches it routinely and considers it acceptable.
The brain, however, cannot be allowed to reach forty-five degrees. The brain requires cooler conditions. The blood travelling to the brain passes through a cavernous sinus — a pool of blood — and alongside this pool run the fine vessels bringing blood from the nasal passages, where panting has cooled it. The warm blood to the brain exchanges heat with the cool blood from the nose. The brain receives cooler blood than the rest of the body.
The body overheats deliberately. The brain does not.
"The body and the brain are operating at different temperatures," the Colonel wrote. "The body stores the heat the brain cannot tolerate. They function, in the Namib, as separate systems. The author, sitting in forty-one degrees attempting to think clearly, finds this arrangement professionally admirable."
He was writing this when the gemsbok walked into the thorn bushes.
Not the edge of the thorn bushes. Into the thorn bushes — specifically into the gap between two large camelthorns that the Colonel could see, from his position, was narrower than the gemsbok's horns by approximately fifteen centimetres.
The gemsbok walked in with complete confidence.