metabolism of the body, it is agreed that the first law of thermodynamics—conservation of energy or constancy of the sum of energy in an isolated system—applies in every respect. Does the second law—irreversible dissipation of energy in one direction—apply to such relatively isolated (adiabatic) systems as a cell enclosed in its cell-wall or the animal body encased in its integument. Does the cell or the organism act like a heat engine or an electric cell, dissipating its energy in one direction, or is it a reversible mechanism, like a dynamo. In the animal body, the food stuffs of high chemical potential, proteids, carbohydrates and fats, are degraded and transformed into substances of low chemical potential (carbon dioxide, urea and water), the energies passing, as in a Carnot cycle, from a source of high potential to a sink at low potential energy. The second law is operative here, but the process is more economical than in a heat engine. Still more economical is it in cold-blooded animals, while in green plants there seems to be an actual reversal of the process, in that substances of low chemical potential (nitrogen compounds, carbon dioxide and water) are transformed into substances of such high chemical potentiality as carbohydrates, proteids and oils. There is thus some indication that in plant cells, or those organisms, like bacteria, which lie between animals and plants, there is a possibility of reversal of those physical processes which take place in inanimate nature. Of this we have further examples in the nitrification of the soils by bacteria buried in it (without the aid of radiant energy from the sun) or in the Brownian movements of bacteria contained in a liquid.[1] Of the possibility of reversing the second law in the human organism Lord Kelvin said that "even to think of it, we must imagine men with conscious knowledge of the future, but no memory of the past, growing backwards and becoming again unborn, and plants growing downwards into the seeds from which they sprang." This would assuredly be an extreme case, but Cushing's production of sexual infantilism in dogs by partial excision of the anterior lobe of the pituitary body fulfils some of these conditions. At best, we can only affirm that the whole matter is transcendental, that is, so far beyond our ken, since it involves an assumption of the old metaphysical "vital principle," which Bergson revamps as the élan vital.
A very complex view of the internal secretions and hormones is that which connects them with the general protective mechanism of the body. The earliest to advance this view was Dr. Charles E. de M. =, of Philadelphia, whose treatise on the internal secretions, published in 1903, has passed through six editions, and has undoubtedly played a prominent part in bringing the subject to a focus in this country. In relation to immunity, Sajous's main position is that the
- ↑ See J. Johnstone, Proc. and Tr. Liverpool Biol. Soc, 1913, XXVII., 1-34.
