constitutes the diathesis must have preëxisted to each of the diseases named, even though it was in no manner obvious to the most careful observer?
Acute, chronic, diathetic, or incubative disease may therefore be regarded as merely expressing the various gradations of morbid processes, from the very rapid to the very slow, from the very severe to the very mild, and from the most readily perceived to the imperceptible.
As acute diseases are only compatible with life for short periods, they are rarely transmitted; in fact, they are excluded from the list of diseases properly inheritable. The open chronic forms of disease, such as scrofula and syphilis, are not unfrequently handed down to the offspring, but far oftener is the heritage of the diathetic grade. This is better tolerated, or more compatible with the continuance of the life in the blood than the open chronic forms which quite commonly render the procreative act abortive.
Before bringing our subject to its practical bearings, it seems necessary that the reader should divest his mind of any vestiges of the glamour of superstition which has so long been around the reproductive process. Darwin succeeds in this with admirable directness by putting reproduction simply as a process of growth. Two cells with somewhat diverse qualities commingle and by gradual accretion develop individual peculiarities. The new self-multiplying stream of blood sometimes appears as if derived in unequal proportions from the two progenitors. This may, however, be supposed to arise from another cause, a temporary or permanent prepotency of the gemnules of one parent over those of the other, which gives them greater activity and power of fission. Be this as it may, every new blood-stream is but a continuation of two older, wonderfully compressed at the junction. The preëxistent forms and forces are only slightly modified by mixture, and by the influence of some variable conditions. In all the general outlines of qualities it is the same blood, exhibiting the same tendencies near or remote to good or to evil, to health or to disease. If there has been a slow struggle—often so subtile as to be at times occult in the parental organism between the tendency to the maintenance of a permanent type and some morbid predisposition—the same is almost certain to be carried on in the blood of the child. The leading causes of any divergence from the continuation of the struggle consist in the crossing of blood, and in the application of modifying conditions when impressibility is at its acme, as from germinal coalescence to adolescence.
With the foregoing facts and deductions in mind, and ranging them around what Dr. Farr terms the great hygienic problem—how to free the people from hereditary disease—the solution does not appear as hopeless and difficult as has been supposed. On the side of release is the great conservative principle of reversion; on the side of continued
