_Nature._ Theories of the nature of this disease are numerous and varied, and are largely based upon some restricted or one-sided view of phenomena and lesions. Coutamine considers it as the reaction of the surplus of nerve force, which was not used up in the easy parturition. The theory is somewhat fantastic as an explanation of the rapidly developing asthenia and paralysis. Billings explains the cerebral anæmia as due to vaso-constriction of the nervous capillaries produced by the exaggerated excitability of the uterine nerves. But with the easy parturition, and delivery, and the moderate contraction of the womb, without violence or spasm, the theory seems rather insubstantial. Trasbot looks on the affection as a congestion of the myelon, apparently shutting his eyes to the far more prominent encephalic symptoms. Haubner considers it as a cerebral anæmia induced by the vaso-dilatation in the portal system and abdominal viscera generally, the result in its turn of the vacuity of the abdomen, from the expulsion of the fœtus and its connections. But the womb is often found contracted and comparatively exsanguine, the plethoric condition of the cow, suddenly increased by the great mass of blood from the uterine vessels, maintains a marked general blood tension, and finally, the closed box of the cranium cannot have its blood so completely drained from it as can a part outside such a cavity. Stockfleth attributed the malady to a metro-peritonitis, and the absorption of the morbid products and poisoning, but neither a metritis nor peritonitis is a common accompaniment of the affection. Franck who accounts for the asthenia by an anæmic condition of the brain, explains the anæmia by a pre-existing congestion and œdema of the rete mirabile at the base of the brain. He claims that sows which have also a rete mirabile in this situation sometimes suffer from parturient fever. He fails to adduce cases in the sheep and goat which also have retia mirabilia. The pregnant sheep may die of an asthenic affection, but usually before parturition. Franck’s theory is plausibly based on the anatomical and physiological conditions, for the elaborate network of vessels at the base of the brain, undergoes great distention under increased arterial tension, and with the serous effusion, compresses the brain and drives out its blood. Palsy of the ganglionic system has been invoked, with succeeding congestion of the myelon and encephalon (Barlow, Kohne, Carsten Harms, etc.). Explanation is made that the supposed excess of nervous force fails of distribution through a lack of conductility of the nerves, and the nerve centres suffer. Binz has even found the spinal roots of the sympathetic surrounded by a thick gelatinoid exudate. The theory is, however, essentially speculative and fails to explain the origin of the disease or its connection with the recognized conditions of its occurrence.