Very much wider departures from the species type are known as mutations. Such variations and mutations, like individuality, may be expressed in qualities which can be weighed and measured, or in function, and all these can be inherited; certain of them known as dominant characteristics more readily than others, which are known as recessive. If these variations from the type are advantageous, they may be preserved and become the property of the species, and it is in this way that the characteristics of the different races have arisen. Certain of the variations are unfavorable to the race. The varying predisposition to infection which undoubtedly exists and may be inherited represents such a variation. Tuberculosis is an instance of this; for, while the cause of the disease is the tubercle bacillus, there is enormous difference in the resistance of the body to its action in different individuals. The disease is to a considerable extent one of families, but while this is true the degree of the influence exerted by heredity can be greatly overestimated. The disease is so common that in tracing the ancestry of tuberculous patients it is rare to find the disease not represented in the ancestors. A further difficulty is that the environment is also inherited. The child of a tuberculous parent has much better opportunity to acquire the infection than a child without such an environment [page 167]. Other diseases than the infectious seem to be inherited, of which gout is an example. In gout there is an unusual action of the cells of the body which leads to the formation and the retention in the body of substances which are injurious. Here it is not the disease which is inherited, but the variation in structure to which the unusual and injurious action of the cells is due.