This permits far more accurate observation and use of environmental factors related to human disease than is possible with unnaturally-confined animals. The human placenta, which is usually discarded after the birth of a child, can be used for practicing techniques of microvascular surgery and for testing toxic side effects of chemicals, drugs, and pollutants. It provides a medium far superior to animal tissues because it is human, and it is entirely without cost. In addition to insulin, growth hormone and interferon can be produced through genetic engineering, and doubtless many other substances as well. Computer models, by means of simulation, provide information that cannot be gained from experiments using living creatures.
Computers also play an integral part in many of the other techniques described here.
They are used, for example, in studies of a variety of anatomical systems, organ functions, in studying heart attacks, and in nerve cell and neuro-muscular research. Computer models of the human circulatory and respiratory systems have been used as teaching devices at a number of medical schools. Computer and mathematical models are based on the use of equations of varying degrees of complexity to represent biological phenomena, and the state of all the elements in the model can be examined at any point in time and their interactions resolved. Computer models are highly accurate and their capabilities are increasing in complexity and scope as the technology is developed. Single cells from human or animals tissues are grown outside the body after separation from their original tissue or organ.