engineering thousands of new plant varieties and animal breeds in the laboratory. As in other manufacturing processes, the primary goal is to increase productivity and lessen labor requirements. To eliminate the cost of insecticides and the labor required to monitor and spray crops, scientists are engineering pest-resistant genes directly into the biological codes of plants. Researchers have isolated and cloned the gene that codes for the toxin in a spore-forming bacterium called Bacillus thuringiensis (Bt) and inserted it into the biological makeup of tobacco, tomatoes, cotton, and other plant crops. The transgenic plants produce a continuous supply of the Bt toxin that kills invading insects. Scientists have also successfully inserted genes into plants that make them resistant to common herbicides. Monsanto has created genetically engineered plants that are resistant to the company’s own herbicide-Roundup. The company has patented the new genetic strains and hopes to market both the patented seeds and the herbicide together as a single package. Other companies are experimenting with transferring genes into plants that make them better able to tolerate drought or extreme heat and cold. Scientists have implanted a frost-resistant gene from a fish into the genetic code of a tomato plant in hopes of conferring frost resistance. The ability to insert specific genes into plants to improve their tolerance to drought, heat, and cold could save billions of dollars in equipment and labor costs by reducing the need to build, install, and manage expensive irrigation systems and frost-protection equipment. Researchers have even transferred nitrogen-fixing genes to non- nitrogen-fixing crops. Molecular biologists look to the day when such genetically engineered crops will substantially reduce the need for nitrogen fertilizers as well as the labor required to manufacture, transport, and apply the chemicals on the soil. Genetic engineering is also being used to increase animal produtivity and reduce labor requirements in animal husbandry. Bovine Growth Hormone (also known as Bovine Somatotropin) is a naturally occurring hormone that stimulates the production of milk in cows. Scientists have successfully isolated the key growth-stimulating gene and cloned industrial portions in the laboratory. The genetically engineered growth hormone is then injected back into the cow, forcing the animal to produce between 10 and 20 percent more milk. Four com- panies, Monsanto, American Cyanamid, Eli Lilly and Upjohn, have spent more than a billion dollars in research and development to bring the controversial product to market.