What the Nose Knows - Avery Gilbert [36]
Because the olfactory cells were tucked away in a narrow olfactory cleft, they did not appear to be exposed to the main flow of air through the nose. Researchers were soon asking how much of air entering the nostrils actually made it to the olfactory nerve endings. Early experiments were ingenious and also a bit macabre. In one study, for example, the head of a cadaver was cut in half and tiny squares of litmus paper were placed throughout the nasal passages. The head was reassembled and ammonia vapor pumped through the nostrils and out the trachea. Color changes in the papers showed that very little ammonia-laden air made it to the sensory cells; most passed through the lower passages. A second, more grotesque experiment anticipated the slice-and-shock art of Damien Hirst by a century. A split cadaver head was pressed against a glass plate and smoke was blown into the nostril. Observers could see the currents and eddies as the smoky air flowed through the complex folds of the nasal chamber. The smoke patterns, like the ammonia vapor, showed that only a fraction of the incoming air made it to the receptors.
Today, sophisticated computer models can simulate nasal airflow. Researchers can see where the flow is laminar (smooth) and where it is turbulent. They can calculate how many scent molecules are deposited onto the sensory surface as air is drawn across it. For all the high-tech apparatus and numerical precision, the modelers reach the same conclusion as their head-splitting predecessors: only about 10 percent of inhaled air blows across the nerve endings in the olfactory cleft.
THE SNIFF—a short inhalation with a high rate of airflow—is an essential step in odor detection. By forcing more air past the olfactory cleft, we take a bigger sample of the external smellscape. So how did it come to be dismissed and even suppressed by serious scientists? This is a strange tale. The first scientist to pay much attention to sniffing was also the one who tried to eliminate it from smell experiments. In 1935, Charles A. Elsberg was a highly regarded neurological surgeon in New York with a flair for invention—he designed surgical instruments and had performed the first successful removal of a herniated spinal disk. Elsberg’s flair for promotion was even bigger. He had cofounded the Neurological Institute of New York, set up the country’s first Neurosurgery Service there, and later cofounded the Society of Neurological Surgeons. At the age of sixty-four, it occurred to Elsberg that brain tumors, by exerting pressure on the olfactory areas at the base of the brain, might lead to impaired odor perception. If he could measure odor sensitivity, he might be able to identify patients with brain tumors. Accordingly, he came up with a method that involved a bottle, a cork, a syringe, and some rubber tubing. The patient would hold his breath and Elsberg would inject odorized air into his nostril. Acuity was measured by how big a blast of air was needed for the patient to detect a smell. Elsberg found that a normal person needed six to nine cubic centimeters’ worth. Elsberg’s system was coldly efficient; it not only eliminated sniffing, it eliminated breathing.
Elsberg touted his method as a major breakthrough: the first scientifically objective measurement of odor sensitivity. He either didn’t know of, or didn’t care to acknowledge, the olfactometer invented thirty years earlier by Hendrik Zwaardemaker. Every sensory psychologist in America was familiar with Zwaardemaker’s device, and most had one in the laboratory. It consisted of a glass sampling tube, curved at one end to fit into a nostril. A wider tube, containing an inner layer of scented material, fit snugly over the sampling tube. The farther the wide tube was pulled back, trombone-like, off the end of the sampling tube, the more scented surface was