Studies show that family members share as much or more of the composition of their microbiota (the trillions of micro-organisms in our guts) with their dogs as they do with each other (Song et. al. 2013). This shows that the introduction of dogs into home environments has a profound impact on the human microbiota. Additionally, many studies show that children raised with dogs are less likely than others to develop a range of immune-mediated disorders, including asthma and allergies (Ownby, Johnson, and Peterson 2002; Almqvist et al. 2003; Havstad et al. 2011). This suggests that dogs can serve as probiotics for children by appropriately training their immune systems not to produce inflammation in response to harmless stimuli. What is not known, however, is whether the same is true for elderly populations and dogs. Thus, this study seeks to explore whether dogs might also improve the physical and mental health of elderly adults by improving the structure and function of their microbiota. The investigators propose a pilot/proof of concept study to investigate whether dogs might improve the physical and mental health of elderly adults via changing (improving) the structure and function of their microbiota (gut flora). The investigators propose a pre-post study design that among 20 elderly individuals (aged 50 and older) to investigate the probiotic effect that dogs might have on these individuals. The investigators are particularly interested to know whether introducing a dog into a home where one has not lived in the recent past increases the "positive" microorganisms in the guts of the humans living with them. The investigators will also measure the changes in markers of inflammation (from blood samples) as well as the changes in self-reported scores of depression, frailty, physical activity, and general health and well-being mobility among human participants. In order to assess any effects in the animal study participants, the investigators will also collect and analyze fecal and blood samples as well as conduct home visits to observe canine and human interactions and bonding and conduct assessments of canine well-being using questionnaires/observational techniques that have been validated for these purposes in other studies. Additionally, the investigators will assess the interactions between of the participants with the dog and how having a dog in the home may influence an individual's relationship with the dog and his/her thoughts about the microbiota, human and canine health and human-animal interactions through monthly semi-structured interviews.