In this article, Katherine Harmon discusses the importance of species-specific microbes for the successful functioning of immune system. The author reports the experiment carried out by Hachung Chung and her colleagues. They tried to raise mice that had only human gut microbiota (1, unpaged). According to the author, human microbes did survive, but the immune system of these mice remained underdeveloped and susceptible to different infections (1, unpaged). The writer refers to the ideas of Hachung Chung who believes that the extensive use of antibiotics alters the microbiome of a human being. As a result, this person may be more likely to suffer from immunological disorders. Overall, Hachung Chung’s study indicates that species-specific microbes are instrumental for the effective work of immune system. Furthermore, this research provides extra-evidence in support of the hygiene hypothesis according to which the lack of exposure to microbes can suppress the development of immune system. According to this article, the mice that were raised in a germ-free environment were much more vulnerable to various diseases, especially in comparison with those mice that were exposed to infections. Yet, their immune system could be strengthened by including species-specific microbes. This evidence can be used to support the hygiene hypothesis. Certainly, the findings of this study cannot be generalized and applied to humans, however, they should be considered by medical workers and drug researchers. When discussing these experiments, Katherine Harmon points out that the use of species-specific microbes can be soon applied in various areas of medicine (1, unpaged). These are the key issued discussed in this article. In my opinion, this article is both informative and interesting. On the whole, the ideas, expressed in this article are supported by other researchers. For instance, Grahame Rook reports numerous epidemiological studies which show that various allergies and autoimmune diseases are more typical of people who have been raised in an extremely clean environment (2, 117). For instance, there are more asthma patients in developed countries, than in developing ones. Certainly, at this point, this hypothesis has not been completely proven, but it helps to explain many epidemiological trends in the world. Although, the findings reported by Katherine Harmon are by no means conclusive, they can throw a new light on this problem. Most likely, similar experiments can soon be carried out. Furthermore, the researcher Michael Schmidt points out that the microorganisms that our body contains are needed for proper response of immune system to various viruses (3, 16). The problem is that antibiotics often kill these microorganisms and the body cannot properly react to various infections. Thus, at the time, when a human body is exposed to a serious threat, the protecting mechanisms do not work as they should do. This is why medical workers should be careful while using antibiotics. Furthermore, the patients should remember that these drugs should not always act as a substitute to immune system. Their abuse can be very dangerous. Thus, one can argue that the issues discussed by Katherine Harmon in her article, are important and evidence-based. This article can be of some interest to people who study biology, immunology or medicine. Overall, this topic has attracte