Science: The Giraffe Problem

Giraffes fascinate physiologists, as well as children at the zoo. The most interesting point about them, physiologically, is that they manage to keep their heads supplied with the proper amount of blood. When a full-grown giraffe lowers its neck to drink and then raises it upright, its head changes level by 19 ft.—from 7 ft. below its heart to 12 ft. above it. Some fancy hydraulics is obviously called for to keep the blood flowing properly at all times.

In the South African Medical Journal, German-born Physiologist R. H. Goetz reports how he solved a part of this problem. He did it one of the hard ways. When he was in Cambridge, England, in 1949, he suggested to Professor de Burgh Daly that they experiment with live giraffes. Daly said, “Bring your own giraffe.” This would have been too expensive, so last year Dr. Goetz assembled a veldworthy laboratory and took it to the northeastern Transvaal, which teems with giraffes.

25-Lb. Heart. Studying dead giraffes was comparatively easy. Dr. Goetz dug a hole in the ground 8 ft. long and filled it with formalin to preserve his massive specimens. Most interesting to Dr. Goetz were the veins and arteries in the giraffes’ long necks. To pump blood so high, giraffes’ hearts weigh 25 Ibs., 40 times as much as human hearts. The jugular vein is more than an inch in diameter, and is fitted with an intricate system of efficient valves. They apparently protect the giraffe’s head from too much blood when its neck is lowered. The hoselike vein also acts as a blood reservoir. It is more or less collapsed when the giraffe’s head is up, so that blood can flow into it at comparatively low pressure when the head is lowered.

Experimenting on live giraffes was more fun, and harder. Dr. Goetz’s original idea was to have an archer pot giraffes with arrows tipped with paralyzing curare, but the giraffes were too skittish, and the arrows did not hit them hard enough to penetrate their inch-thick hides. So Dr. Goetz spiked rifle bullets with curare mixed with powdered sugar, and shot them into a giraffe’s hindquarters. In 45 minutes the muscles were paralyzed. Then Dr. Goetz and his safari mates hobbled the giraffe’s legs, put a blindfold over its eyes, and erected around it three tons of builders’ steel scaffolding. When all was secure, he injected a curare antidote. The paralysis disappeared, but the giraffe found itself in a cage and at the doctor’s mercy. These precautions were necessary, Dr. Goetz explains solemnly, because giraffes, besides being rather dangerous animals, are extremely sensitive and subject to fainting fits.

12-Ft. Catheter. With his giraffe securely caged, Dr. Goetz listened to its 25-lb. heart and located the carotid artery, which runs up the neck. He made an incision in the hide, opened the artery and applied a specially built manometer (blood-pressure-measuring instrument) with a catheter 12 ft. long. On its tip was a bit of radioactive cobalt, so its progress could be followed with a Geiger counter as it moved up the artery.

The manometer gave data that had never before been measured. When the giraffe’s head was up. the blood pressure was 200 mm. of mercury at the base of its brain (v. 120 mm. in a healthy human subject). When the head was lowered, there was no rush of blood to the brain.

The pressure actually dropped to 175 mm. Obviously the giraffe’s system of valves is highly efficient against violent changes of hydrostatic conditions.

Dr. Goetz believes that “we have only touched the fringes” of the giraffe problem. Next time he goes on safari, he will be equipped with better apparatus. When giraffes are fully understood, he hopes, something constructive can be done for human jet-plane pilots, who suffer from the changes of blood pressure that giraffes avoid.