_Idiosyncrasy. Constitutional Predisposition._ This must be allowed, inasmuch as that it covers all those individual conditions, functional and structural, which belong to the heavy milker, or the animal with extraordinary powers of digestion and assimilation. The same shows in the predisposition to a second attack of an animal which has survived a first one. The structural changes in the nerve centres, which occur in the primary attack, leave traces, which render these parts more susceptible at the next calving. In my own experience the violence of the disease is liable to increase with successive attacks, so that a second or third cannot be hoped to be as mild as was the former one. _Cardiac Hypertrophy._ Cagny draws attention to the fact that in man and beast alike the heart undergoes hypertrophy during gestation and, above all, during its later stages. In improved breeds of cattle, and especially in milking breeds, a great development of the whole circulatory system is seen, and a large heart is a constant feature of this. This implies an increased force of cardiac systole, an increased blood tension in the arteries and capillaries, a condition which tells with special force on the soft tissues of the brain, as the violent abdominal compression in the expulsive efforts of parturition, tends to drive the blood from the great vascular viscera situated back of the diaphragm. _Parturition_ and the subsequent _contraction of the womb and expulsion of the great mass of blood_, must be accorded a prominent place among causative factors. The disease is almost restricted to the first week after parturition, and its gravity is greater the more it is related to the parturient act. Cases occurring in the first three days are usually fatal. The gravid uterus contains a very large amount of circulating blood, and when the womb contracts, the greater part of this is suddenly thrown upon the general circulation, already plethoric to an undue extent. As yet the mammæ are congested and there is no free depletion through that channel, so that there is a marked temporary plethora and vascular tension, before the system can establish free elimination and, as it were, strike a healthy balance. In this period of transient plethora there lies a source of great danger to the general system and, more particularly, to the brain. _Emotional Excitement_ connected with the removal of the calf is urged by Günther, Jaumain, Félizet and others as a prominent cause. This, however, must be rare, at the most; the disease does not attack the primipara that should be most susceptible to this influence, but the mature animal, at her third calving or later when she is already well accustomed to this treatment; it supervenes so quickly on parturition in many cases, that there was no opportunity for such emotion; it occurs also in cows, the calves of which have remained with them or have received no attention from them.