the temperature, paralyzed parts are invariably lower, as proved by Dunglison and by Earle, who found a difference of 22°, which was lessened 7° by an electric current. Those remarkable cases of great elevation of temperature after death by cholera and yellow fever, prove the influence of the nervous system not to be essential. The increase occurred between the periods of somatic and molecular death. The nervous system then can control, though it does not generate heat-just, as Draper remarks, the engineer of the locomotive can regulate, though he cannot produce heat; and if he be removed, or the nerves divided, all regulation of temperature ceases. Nervous influence may prevent the indiscriminate removal of all particles the destroying oxygen meets with. Draper appeals to the following facts in physics as showing a similar controlling action :-if a plate of zinc and one of copper be kept apart in acidulated water, no voltaic action goes on, but at once occurs if they are connected by a conducting wire. Newly made lamp-black will ignite spontaneously on exposure to air; whereas diamond, chemically identical, but allotropic, is quite unchangeable. There may be allotropism of organic bodies under the control of the nervous system. Cooling Influences are, of course, necessary to preserve the uniform temperature of the human body. Heat is lost (1) by radiation from the skin and its contact with air, from 30 to 50 degrees colder at least in our climate than the body. Man's reason has taught him to regulate this by placing bad conductors, as warm clothing, on his surface; (2) by evaporation, there being lost by cutaneous and pulmonary surfaces some 3 or 4 lb of water daily; this powerful cooling agency, however, varies much with the hygrometric state of the atmosphere. The dark surface of the negro absorbs the heating rays of the sun, and thus, by great evaporation, can sustain a climate intolerable to others. The lady's fan does not propel colder air against the face, but merely promotes evaporation by fresh portions of air. Chabert, "the fire-king," Blagden, and the workmen of Sir F. Chantrey, the sculptor, have borne extraordinary temperatures, the former having entered a chamber of which the temperature was between 400° and 600°. The air should be dry, for if moist, no evaporation was allowed, and such heat was intolerable. The band, if damp, may be put into molten metals, for a layer of spheroidal particles of water intervenes, and prevents any great rise of temperature. 3. The air we breathe abstracts heat from the nasal bronchial and pulmonary surfaces, and thus affords another cooling agency, having the advantage of raising the temperature of the air to a degree which will not chill the pulmonary capillaries. When cold air is admitted by an opening in the trachea, made suicidally or by the operative surgeon, fatal bronchitis is often excited. The fatality of the same disease in infancy and old age, when calorific power is not energetic, is well known. Light is another physical agent which is believed to influence the development and other nutritive changes of animals. It was asserted in 1824 by W. F. Edwards, that the tadpole, if deprived of light, did not become developed into the perfect frog. This statement, however, cannot be now accepted as true, as Mr. Higginbotham and Dr. R. M'Donnell have conducted some most interesting experiments, which prove that the arrest of developmental change is due to the low temperature and absence of oxygen and proper vegetable and animal food, rather than to the denial of light. The latter has discussed the whole subject in an able paper in "Le Journal de la Physiologie, No. d'Octobre, 1859." Elevation of temperature hastens the metamorphosis, and in this way the heating rays of the sun may have some slight influence. In the same memoir he also shows the homology of the swimming bladder of fishes to the lungs of higher vertebrates. The pigmentary matter of the blood and of tissues, which is probably derived from it, is not fully developed in man or animals deprived of light; but as in such cases there is usually also a deficiency of oxygen, the effect may be due to the latter agent. Darkness is usually considered to be favourable to the fattening of cattle and geese, as seen in the cruel expedient they adopt in Strasburg to increase the bird's liver, for making the "patie de foie gras." Other animals, however, seem induced to eat excessively if strong light is made to alternate with darkness; and the manner in which Italian gourmands employ this principle for the fattening of ortolans, is amusingly narrated in the work on Italy of our brilliant countryman, the Right Hon. Mr. Whiteside. QUESTIONS FOR EXAMINATION. JUNIOR. 1. Describe the structure of the trachea? 2. What muscles produce inspiration? and describe the action of three of the most efficient. 3. What terms have been applied to the quantities of air which can be expelled from the lungs by various degrees of force? 4. State the components of ordinary air, and the purpose of its most important elements. 5. Describe the ways in which various modes of suffocation produce death. 6. What animals undergo hybernation, and what are its phenomena? 7. How is heat generated, and how regulated in the human body, especially when it is exposed to excessive temperatures? SENIOR. 1. Describe the ultimate terminations of a bronchial tube. 2. Explain physiologically sighing, coughing, and sneezing. 3. What changes does air undergo by respiration, and offer proofs to show where its constituents suffer chemical action. 4. Arrange in parrallel columns the circumstances which increase or decrease the evolution of carbonic acid by the lungs. 5. Give some examples of variations of external temperature, and the effects of disease on the temperature of the human body. 6. What are the other decarbonizing surfaces besides the lungs ' 7. What effects have light been supposed to produce on animals, and how have the results been shown to be fallacious? 177 SECRETION. SECRETION is that process by which matters are separated from the blood, and such products are either excrementitious or useless, recrementitious or useful The former are often termed excretions. Like the analogous act of nutrition, the appropriation of the special material is effected by cells lining the interior of each special gland, which drains its peculiar secretion from the blood, and their very great variety illustrates the very complex nature of that fluid. Some fluids which merely ooze through the coats of the capillaries, are termed exudations or exhalations, but there are no special" exhalents" as once believed. The retention of the materials of the excretions is injurious, or will even destroy life, as when the kidney is removed from animals. The chief excretions are water and carbonic acid from the lungs and skin, urea and other nitrogenized substances from the kidney, lactic acid and various salts from the skin and kidney, and many matters discharged from the liver and other alimentary glands with the fæces. The excretions thus afford examples of the gaseous, liquid, and solid states. The most remarkable recrementitious products are, saliva, gastric and pancreatic juices, some elements of bile, the cutaneous secretions, and those connected with reproduction, as semen, milk, &c. One fluid may con tain both recrementitious and excrementitious materials— for instance, the bile; or as regards its composition may be excrementitious, yet in being discharged may fulfil a useful purpose-as sweat, which cools the body by its evaporation. One gland by increased activity may compensate for the secretion of another being checked-and this is termed "vicarious secretion." It shows that special cells are not required to separate each material, for we find urea, cholesterin, and other matters which exist preformed in the blood, in many various secretions. There are, however, other substances which can be only generated in each special gland out of elements afforded by the blood. Many substances, as ferrocyanide of potassium, lactate of iron, sugar, &c., show a preference for some glands, either not passing, or passing very slowly, through others; and much the same might be said of various kinds of membrane in regard to dialysis through them. Uniformity of structure and development, as inflections from the skin or mucous membrane, indicate probably similarity of function, and suggest that vicarious secretion may take place. The best example of this occurrence is afforded by Dr. Laycock's cases, amounting to 124, where urine was discharged from What are termed conglobate glands are merely convoluted tubes communicating with each other. Such are the lymph and ductless glands; and as they have no excretory duct, they must pour their products into the circulating current. Conglomerate glands are inflections from the skin or mucous surface, much branched and lined by the globular form of epithelium, which selects the materials of the secretion proper to each gland. These cells develop from the granular state, and when filled with the secretion burst into the excretory duct. The parotid, the structure of which is represented at p. 71, is a good example of the conglomerate gland. Many physiologists attach importance to the size of the capillaries of each gland, as they think the straining off of each special matter can be thus accounted for. The duct is often muscular, may be distended into a temporary reservoir, and is usually single; those of breast, lacrymal, tonsil, sublingual, and pros |