V.

The great nervous prostration and the lack of energy which were observed among the prisoners, were not due entirely to climate. The activity of the nervous mechanism depends greatly upon the supply and purity of the arterial blood. It is the same with the nerve fibres as with the nerve centres, but in less degree. We observe that the exaltation and depression of the nervous power are within the control of man by the administration of certain drugs, or respiration of appropriate gases. The accumulation of bile or urea in the blood diminishes the nerve energy. Many physiologists enumerate moral depressions among the principal causes of epidemics; and this opinion is not strange when we consider how completely the system is under control of the nervous influence, and how much the supply of oxygen and blood to the organs and tissues depend upon the nervous power; and how much, moreover, the integrity of the nervous system depends upon the purity of the blood.

In the process of starvation, during the struggle for life, the hidden forces in reserve--the superabundant muscle, fat, tissues, even the brain-substance--are gradually absorbed. The volume of blood may remain the same, but the vivifying particles which circulate in the vital stream are rapidly consumed by the wants of the wasting economy, and disappear. And when these hematic globules are lessened to a certain limit below the normal proportion death ensues. Vierodt has discovered that the limit of this singular law is 52 per 1000 for the dog, and about 60 per 1000 for some other species of the mammalia. The physiologists have shown how the vivifying principles acquire vigor through the blood discs, and how these, when absorbing pure oxygen through the pulmonary circulation, contribute to the development of muscular fibre and the nervous material. Mammals and birds, when deprived of food, die in ten to twenty days, losing from one third to one half of their weight.