Final answer:
The use of live animals and bird embryos is a classical method for virus propagation, often used when viruses do not grow well in cell cultures.
Step-by-step explanation:
Live Animals and Bird Embryos are considered a classical method to propagate viruses. This classical method has been used for many years in virology. By infecting live animals or bird embryos, researchers can cultivate and study viruses in a laboratory setting. While these techniques are foundational, over time, cell culture techniques have become more prevalent due to ethical concerns and the efficiency of in vitro systems. Nevertheless, the use of animals and embryos is still relevant for certain applications where cell cultures are not sufficient, such as for viruses that do not grow well in cell cultures or for studying the full immune response.