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.

While tuberculosis and gout represent instances in which, although the disease itself is not inherited yet the presence of the disease in the ascendants so affects the germinal material that the offspring is more susceptible to these particular diseases, much more common are the cases in which disease in the parents produces a defective offspring, the defect consisting in a general loss of resistance manifested in a variety of ways, but not necessarily repeating the diseased condition of the parent.  In these cases the disease in the parents affects all the cells of the body including the germinal cells, and the defective qualities in the germ cells will affect the cells of the offspring which are derived from these.  There is a tendency in these cases to the repetition in the offspring of the disease of the parents, because the particular form of the parental disease may have been due to or influenced by variation of structure.  One of the best examples of affection of the offspring by diseased conditions of the parents produced by a toxic agent which directly or indirectly affects all the cells of the body is afforded by alcohol when used in excess.  Since drunkenness has become