_Scorbutic_ diseases, _i.e._, Scurvy and Purpura, are characterized by a general poorness of the blood, with a special deficiency in the amount of Fibrine and of salts. There is a general tendency to hæmorrhage and ulceration all over the body. It has been observed that these diseases seldom occur in persons who are accustomed to a natural and mixed diet. _Periodic_ disorders are known to be attributable to the entrance into the blood of a peculiar aerial poison. The mild malaria of England excites a comparatively tractable ague; that of the Maremma and of the Pontine Marshes, in Italy, brings on very fatal fevers; while the remittents that are due to the exhalations from the ground on the West coast of Africa, and in the West Indian Islands, are of a still more virulent nature. Accurate observations have shown that they are all caused by the exposure of the system to this poison, and by its working in the blood. With _Convulsive_ disorders there is more difficulty. Although these diseases are manifested either by a derangement of the nervous system in general, or by a disturbance of the functions of the brain or spinal cord in particular, yet they are very rarely accompanied with an appreciable nervous lesion. When this is the case, as in the instance of Tetanus, which may arise from a mere irritation of the end of a nerve, they are extremely intractable, and are not at all under the influence of those blood-medicines which are useful in other cases. Epilepsy, too, may sometimes be due to a bony spicula or tumour in the brain, or to the irritation produced by intestinal worms in children; but these direct nervous causes of such convulsive disorders are to be considered as the exception, and not the rule. For they are more often connected with a diseased condition of the blood.