The design of the cage or primary enclosure can greatly influence the animal's environment. The environment in the cage (the micro-environment) may differ from the environment of the animal room (the macro-environment). Some of the newer caging systems for rodents, for example, incorporate a microbiological barrier. This may result in substantially higher temperature, humidity, carbon dioxide and ammonia levels in the cage than in the room. Since such factors may adversely affect research results as well as animal health, they should be considered in the experimental design and animal housing.