the most interesting points in its anatomical history relates to its mode of development. This, however, does not present any great physiological importance, and is fully treated of in works upon anatomy."

Pituitary Body and Pineal Gland.

These little bodies, situated at the base of the brain, are quite vascular, contain closed vesicles and but few nervous elements, and are sometimes classed with the ductless glands. Physiologists have no idea of their function.

The pituitary body is of an ovoid form, a reddish-gray color, weighs from five to ten grains, and is situated in the sella turcica of the sphenoid bone. It is said to be larger in the fœtus than in the adult, and at that time has a cavity communicating with the third ventricle.' Ecker describes it as containing the elements of a blood-gland.' This little body has lately been studied by M. Grandry, in connection with the suprarenal capsules. He regards it as essentially composed of closed vesicles, with fibres of connective tissue and blood-vessels. The vesicles measure from to of an inch in diameter. They are formed of a transparent membrane, containing irregularly polygonal, nucleated cells, and free nuclei. The cells are from too of an inch in diameter. The nuclei are distinct, with a well-marked nucleolus, and measure about of an inch. Capillary vessels surround these vesicles, without penetrating them. M. Grandry did not observe either nerve-cells or fibres between the vesicles. In old subjects he found the peculiar concre

1 For the history of the development of the thymus, the reader is referred to special treatises. A very full account of its development is given by Dr. Handfield Jones, in the Cyclopedia of Anatomy and Physiology, London, 18491852, vol. iv., Part ii., p. 1087, et seq.

2 GRAY, Anatomy, Descriptive and Surgical, Philadelphia, 1862, p. 519.

3 ECKER, in WAGNER, Handwörterbuch der Physiologie, Braunschweig, 1853, Bd. iv., S. 161.

4 GRANDRY, Glande pituitaire.—Journal de l'anatomie, Paris, 1867, tome iv., p. 400, et seq.

tions (sympexions) already described as existing in the thy

roid.'

The pineal gland is situated just behind the posterior commissure of the brain, between the nates, and is enclosed in the velum interpositum. It is of a conical shape, onethird of an inch in length, and of nearly the color of the pituitary body. It is connected with the base of the brain by several delicate commissural peduncles. It presents a small cavity at its base, and frequently contains in its substance little calcareous masses, composed of phosphate and carbonate of lime, phosphate of magnesia and ammonia, and a small quantity of organic matter. It is covered with a fibrous envelope, which sends processes into its interior. As the result of the researches of M. Grandry, it has been found to present a cortical substance, entirely analogous in its structure to the pituitary body, and a central portion, composed of the ordinary nervous elements found in the gray matter of the brain. Its structure is regarded by Grandry like that of the medullary portion of the suprarenal

as very

capsules.'

2

It is difficult to classify organs, of the function of which we are entirely ignorant; but the structure of the little bodies just described certainly resembles that of the ductless glands. We have only indicated their anatomy to show that their function is probably analogous to that of the other organs of the same class.

1 See page 360.

2 GRAY, op. cit., p. 528.

3 GRANDRY, Glande pinéale.-Journal de l'anatomie, Paris, 1867, tome iv., p. 405, et seq.

CHAPTER XII

NUTRITION.

Nature of the forces involved in nutrition-Protoplasm-Definition of vital properties-Life, as represented in development and nutrition-Principles which pass through the organism-Principles consumed in the organism— Nitrogenized principles-Development of power and endurance by exercise (Training)-Non-nitrogenized principles-Formation and deposition of fat -Conditions under which fat exists in the organism-Physiological anatomy of adipose tissue-Conditions which influence nutrition-Products of disassimilation.

NUTRITION proper, in the light in which we propose to consider it in this chapter, is the process by which the phys iological decay of the tissues and fluids of the body is compensated by the appropriation of new matter. All of the physiological processes that we have thus far studied, including circulation, respiration, alimentation, digestion, absorption, and secretion, are to be viewed in the light of means directed to a single end; and the great function, to which all the others are subservient, is the general process of nutrition.

The nature of the main forces involved in nutrition, be it in a highly-organized part, like the brain or muscles, or a tissue called extra-vascular, like the cartilages or nails, is unknown. The phenomena attending the general process, however, have been studied most carefully, and certain important positive results have been attained; but we find no more satisfactory explanation of the nature of the causative force of nutrition in the doctrines of to-day than in the speculative theories of Pythagoras.

We can hardly realize the vast extent of the problem of nutrition from a review of the functions which we have already considered. We have seen that the blood contains all the elements that enter into the composition of the tissues and secretions, either identical with them in form and composition, as is the case with the inorganic principles, or in a condition which allows of their transformation into the characteristic principles of the tissues, as we see in the organic substances proper. These materials are supplied to the tissues, in the required quantity, through the circulatory apparatus; and the oxygen, which is immediately indispensable to all the operations of life, is introduced by respiration. The great nutritive fluid, being constantly drawn upon by the tissues for materials for their regeneration, is kept at the proper standard by the introduction of new matter into the system, in alimentation, its elaborate preparation by digestion, and its appropriation by the fluids by absorption. These processes, many of them, require the action of certain secretions. The introduction of new matter, so essential to the continuance of the phenomena of life, is demanded, on account of the change of the substance of the tissues into what we call effete matter; and this is discharged from the animal organism, to be appropriated by vegetables, and thus maintain the equilibrium between these two great kingdoms in Nature.

What is it that causes the parts of a living animal organism to undergo change into effete matter, incapable of any further animal functions; and what is it that gives to these parts the power of self-regeneration, when new matter is presented under proper conditions?

These questions are the physiological ignis fatuus, which, it is to be feared, will forever elude the grasp of scientific inquiry. They constitute one of the great mysteries ever present in the minds of the student of Nature, and one, the grandeur of which is so immense that it is a problem with which our intelligence can scarcely grapple. Its greatness is com

mensurate with that of the question of the soul, and its reiations to the finite and the infinite; a question which philosophers have been constrained either to admit upon the faith of revelation, or to hopelessly abandon. Little, if any, real progress is to be made by endeavoring to cover the inscrutable problem of life with a simplicity entirely artificial. This will always be attractive, and, to a certain extent, satisfactory to the minds of those unacquainted with the details of natural laws, or willing to admit speculative theories upon subjects concerning which it is impossible, in the present condition of science, to have any positive information; and, if generally admitted by biological students, would carry our science back to the dark periods in its history, when the study of Nature was confined to speculation, and there existed no knowledge based upon the direct observation of phenomena. A new name, arbitrarily applied to organic matter, without any addition to its physiological history, does not advance our definite knowledge. For example, it has long been known that certain nitrogenized constituents of the organism, classed collectively as organic principles, seem to give to the tissues their property of self-regeneration and development. It may seem to those not engaged in scientific inquiry that a recital of the wonderful properties of "protoplasm" affords some additional information concerning the phenomena observed in organized bodies; but the true definition of the term leads us back to our former ideas of the so-called vital properties of organic matters.'

It is a well-established fact that while nearly all of the tissues undergo disassimilation, or conversion into effete matter, during their physiological decay in the living organism, others, like the epidermis and its appendages, are

1 HUXLEY, The Physical Basis of Life, New Haven, 1869,-from the Fortnightly Review, for February, 1869. This very interesting and able discourse, delivered originally before a popular audience, is referred to, not as a subject for rigid scientific criticism, but as formularizing some of the prevalent ideas concerning the properties of the so-called protoplasm.