This condition has a name in medical writings, from a Greek word expressive of the blue tint which characterises it, and is called _cyanosis_. It depends on the blood not having undergone completely those changes in the lungs which take place in the healthy state. The blood, as it returns through the veins to the right side of the heart, is of a deep purple hue. The right side of the heart contracting sends it to the lungs, where, in the minute vessels of the air-cells, it is purified, and returns vivified by the oxygen a bright scarlet stream, to be distributed by the arteries over the whole body; and thence to return once more for fresh purification to the right side of the heart. Before birth, the blood does not run the same course, but is purified within the mother's body, the blood running through channels which close with the first breath the infant draws. The previously existing communication between the two sides of the heart ceases at the same time as the new channels are opened, by the shutting of a thin valve which had hitherto allowed the blood to pass from one side to the other. Sometimes this closure fails to take place, or takes place but imperfectly; sometimes, in addition, the channels which should be disused after birth remain open still; and sometimes also the heart is otherwise imperfectly formed, and a large communication exists between the two sides of the heart, which long before birth ought to have been firmly partitioned off from each other. According to the freedom of communication between the two sides of the heart, there is more or less ready intermingling of the impure blood with that which is already purified; and this is betokened by the greater or less severity of the symptoms which I have described. When the heart is very malformed, and the blood consequently is very impure, life is but a short agony which ends in a few weeks; some slight movement, some little accidental cold deranging altogether the imperfect machinery, and bringing it to a sudden standstill. Between this and the slightest cases there are all shades of difference, till, in the latter, a smaller power to maintain warmth, a less rapid growth, a smaller muscular development, a feebler power, a hurry of breathing on exertion, or in ascending a hill, or in going up a staircase, are all, except the sounds which the educated ear detects of the blood passing through its devious course, that tell of nature having, in this instance, ill done her handiwork.