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Another method is tissue culture. Bits of cancer tissue are stuck to the side of a test tube. A nutrient solution (made of such unlikely ingredients as extract of human placentas) is added. The tube is sealed and put on a vertical merry-go-round in an incubator. As the merry-go-round revolves slowly, the solution washes over the cancer tissue, which grows vigorously just as if it were in a living body. Drugs can be tested against it simply by adding them to the solution.
Sloan-Kettering now has 2,300 chemical agents on file, and has already tested some 1,500. Six of them proved to have a good "differential effect" against one or more types of mouse cancer. A couple of dozen had some lesser effect. According to Dr. C. Chester Stock, head of the Division of Experimental Chemotherapy, this record is by no means discouraging. As the records and experience accumulate, the scientists are learning how to predict whether a compound is worth testing. If a new one has a slight effect, one of its close relatives may prove better. And each slightly successful drug sets biochemists to figuring out why it worked at all.
Cell City. Long-range figuring-out is the duty of such men as Dr. George B. Brown, head of the Protein Chemistry Division. Dr. Brown and his assistants are studying the chemistry of both normal and cancer cells, looking for differences that they may exploit.
Cell chemistry is a maddeningly complicated study. It is known that cells contain certain chemicals, but they are not mixed together haphazardly like dissolved salts in a chemist's beaker. Each cell is like a great, complex metropolis. The individual citizens (atoms) are organized into intricate groups like the people of the city. Some groupings (e.g., the three-atom molecule of water) are as small and tight as families. Others are larger, like all the workers in one factory. The various groups interact constantly, their links forming and dissolving as the cell lives and grows. Certain single large molecules (analogous to the city government) are thought to affect all the cells.
To get the most rudimentary understanding of the workings of the living, changing cell is enormously difficult. It would be even harder without a new tool: nitrogen 15, a stable (nonradioactive) isotope of nitrogen. Chemically, nitrogen 15 is exactly like the common nitrogen 14. The cells cannot tell the difference. But since it is slightly heavier, nitrogen 15 can be measured accurately by a balky and expensive instrument called a mass spectrometer. If compounds containing nitrogen 15 instead of ordinary nitrogen are fed to cells, the scientists can tell with the mass spectrometer whether the cells have accepted them as food.
Such work is slow and expensive: nitrogen 15 costs $1,000 for a single study. But already Dr. Brown's group have had one outstanding, success in their study of a cell's reproductive system. They used an artificial compound called 2,6-diaminopu-rine, not yet isolated in nature, which they thought had a momentary existence inside the cell. The organic chemists synthesized some of this compound and turned it over to the chemotherapists. They thought that it might have the sought-for "differential effect" on lawless cancer cells.