Today, scientists find useful applications for compounds from nature but their search methods have changed. Biochemists analyze plants, microorganisms, but many of the things they work with are small even to be seen with a microscope, so they use chemicals to perform experiments. Many of these new inventions are enzymes, biological molecules that are like catalysts for chemical reactions. Sometimes, the only way to get useful organic compound is to get the organism that contains it. But improvements in science, useful compounds can now often be reproduced in a laboratory and sometimes they can be made by genetic engineering. For examples, insulin is a hormone important to human digestion. Many people with diabetes must take insulin as a medicine. The impact factor of journal provides quantitative assessment tool for grading, evaluating, sorting and comparing journals of similar kind. It reflects the average number of citations to recent articles published in science and social science journals in a particular year or period, and is frequently used as a proxy for the relative importance of a journal within its field. It is first devised by Eugene Garfield, the founder of the Institute for Scientific Information.