Part 156
It is found that, under ordinary circumstances, evaporation is confined to the surface of the heated liquid, and is therefore slower or quicker, in proportion to the extension of that surface. Hence has arisen the adoption of wide, shallow vessels for containing fluids during their exposure to heat for this purpose. Evaporation proceeds most rapidly when a current of air (especially hot and dry air) is made to pass over the surface of the fluid; as, in this ease, the vapour is prevented from resting upon the surface, and impeding the process by its pressure. For a similar reason, liquids evaporate more rapidly in vessels partially covered than in open ones. In the former case the cool incumbent air condenses and throws back a portion of the vapour, which thereupon, besides its cooling action, offers mechanical resistance to the diffusion of the vaporous particles as they arrive at the surface of the liquid. In the latter case these obstacles are avoided, and the impetus of the vapour pouring forth from a contracted orifice (or pipe), not only readily overcomes the pressure of the atmosphere, but offers less surface for its cooling action, until it has passed much beyond the points at which it can exert any influence on the fluid from which it has escaped. In this way the chemical action of the atmosphere on the liquid operated on is also considerably lessened. On the small scale, shallow capsules of glass, wedgwood-ware, porcelain, or metal, are commonly employed as evaporating vessels, and these are exposed to heat by placing them over a lamp, or naked fire, or in a water bath, or sand bath, according to the temperature at which it is proper to conduct the process. On the large scale, high-pressure steam is usually employed as the source of heat. The term 'spontaneous evaporation' is applied to the dissipation of a fluid by mere exposure in open vessels, at the common temperature of the atmosphere, and without the application of artificial heat. The celerity of this species of evaporation wholly depends on the degree of humidity of the surrounding air, and differs from the former, in which the rate of evaporation is proportionate to the degree of heat at which the process is conducted, and the amount of pressure upon the surface of the liquid. Evaporation '_in vacuo_' (as it is called) is conducted under the receiver of an air-pump, or in an attenuated atmosphere, produced by filling a vessel with steam, by which means the air is expelled, when all communication with the external atmosphere is cut off, and the vapour condensed by the application of cold. Fluids are also evaporated in air-tight receivers over sulphuric acid, by which they are continually exposed to the action of a very dry atmosphere. When such a receiver is connected with an air-pump in action, evaporation proceeds with increased rapidity, and intense cold is produced. It appears, from the experiments of Dr Ure, that "if the bottom of a pan, and the portion of the sides immersed in a hot fluid medium (solution of chloride of calcium, for example), be corrugated, so as to contain a double expanse of metallic surface, that pan will evaporate exactly double the quantity of water, in a given time, which a like pan, with smooth bottom and sides, will do, immersed equally deep in the same bath. If the corrugation contain three times the quantity of metallic surface, the evaporation will be threefold in the above circumstances. But if the pan, with the same corrugated bottom and sides, be set over a fire, or in an oblong flue, so that the current of flame may sweep along the corrugations, it will evaporate no more water from its interior than a smooth pan of like shape and dimensions placed alongside it in the same flue, or over the same fire."
In the laboratory, steam heat is now almost exclusively employed. Copper, or tinned, glazed, or silvered coppered pans, boilers, and stills, are surrounded by a 'jacket' of cast iron, and high-pressure steam admitted between the two. By due management of the supply-cock, a range of temperature may be thus obtained extending from about 90° to 325° Fahr.
It is found that, under ordinary circumstances, 10 square feet of heated surface will evaporate fully 1 lb. of water per minute; and that a thin copper tube exposing 10 feet surface will condense about 3 lbs. of steam per minute, with a difference of temperature of about 90° Fahr. This is equal to 30° Fahr. per lb.; and, consequently, the heat of the steam employed to produce the evaporation should be 212° + 30° = 242° Fahr.
An attention to the facts and principles thus briefly explained above will be found of great value in the laboratory.
=EXCIP'IENT.= See PRESCRIPTION.
=EXCI'TANTS.= See STIMULANTS.
=EXCORIA'TIONS.= _Syn._ _Sprays_, CHAFINGS.
In _surgery_ and _pathology_, superficial injuries or affections of the skin, consisting of the removal of the scarf-skin or cuticle, accompanied with more or less irritation and slight inflammations. When arising from rough friction or attrition, they are more commonly called abrasions. Young children are very apt to be chafed under the arms, behind the ears, between the thighs, and in the wrinkles and folds of the skin generally, unless great attention is paid to cleanliness, and wiping the skin perfectly dry after washing them. Whenever there is a tendency to excoriations of this kind, either in adults or children, a little finely powdered starch, or violet powder, applied by means of a puff, or a small bag of muslin, once or twice a day, will generally remove them, and prevent their occurrence in future. Mild unguents, as cold cream, or spermaceti cerate or ointment, may also be used with advantage. The preference should, however, be given to the remedies first named, from their not soiling the linen. See ABRASION.
=EXCRETA.= The excrementitious matter evacuated from the bowels varies of course in composition and quantity according to the food from which it is derived.
Berzelius found a sample analysed by himself to yield about seventy-five per cent. of water, the remainder being made up of alimentary waste, and biliary matter. A large amount of phosphates of calcium and magnesium was found in the ash remaining after the incineration of the solid matter. A specimen of fæcal matter examined by Playfair yielded 15 per cent. of nitrogen and 45 per cent. of carbon. Marcet states that he has obtained from excrement a crystallisable body possessing an alkaline reaction; to which he gives the name _excretin_; also a fatty substance, which he terms _excretolic acid_. To excretin he assigns the formula C_{7}_{8}H_{1}_{5}_{6}SO_{2}; the composition of the acid has not been determined.
Hinterberger has succeeded in getting excretine (excretin), free from sulphur, and gives as its simplest formula C_{2}_{0}H_{3}_{6}O; which shows a close resemblance to cholesterin, C_{2}_{6}H_{4}_{4}O.
But cholesterin is less easily dissolved in vinegar than excretin, and the solution deposits crystals which, when viewed by the microscope, are found to be beautiful silky six-sided prisms, while the excretin solution yields round masses.
Treated with bromine, excretin gave a crystalline body having the formula C_{2}_{0}H_{3}_{4}Br_{2}O; but the author did not succeed in preparing a chlorinated compound of excretin.
In the excreta of carnivorous animals no excretin has been discovered, although a substance resembling it has been found. Cholesterin has been obtained from the fæces of the crocodile, but no urates; whilst the excreta of the boa contain urates, but are destitute of cholesterin.
The fæces of animals that live on vegetables contain neither excretin, butyric acid, nor cholesterin.
The excreta of birds and serpents, which mixed with the secretion from the kidneys, are discharged from the animals by the cavities, are very similar to urine, and consist chiefly of alkaline urates and earthy phosphates.
The excrements of insects consist mainly of the remnants of the tissues, animal or vegetable which they have swallowed as food, mixed with constituents of the urine, provided the insect has no special urinary organs.
Briéger examined the fæces of healthy persons, and of convalescents, and found in addition to acetic, butyric, and isobutyric acids, small quantities of phenol and indol, and a new crystallisable body, which he terms _skatol_ (_skatos_, fæces). It crystallises in irregular-dentate shining plates, resembling indol, which by frequent recrystallisation from hot water, can be obtained snow white. Skatol forms the chief constituent of the volatile aromatic components of human fæces. Fæces of dogs (whether fed on meat or bread diet) contained no skatol, but indol, and in addition a yellow oil, with a revolting and peculiarly irritating smell.
Briéger has not yet been able to analyse this yellow oil, although it forms the chief volatile constituent of dogs' fæces. He has repeatedly obtained it from distillation from human pathological fluids. In the pancreas after putrefaction, and in the fæces of typhus patients, no skatol was found. The author considers skatol identical with the substance which Secretan obtained by the decomposition of egg albumen under water for six months.
Skatol injected under the skin of rabbits, passes out in the urine as a substance yielding colouring matter. Skatol is believed by the author to be the substance in human urine which, according to Jaffé, yields a red or violet colour on the addition of hydrochloric acid and chloride of lime.
Phenol, the author finds, is a constant component of human fæces. The above results show that specific products of decomposition are normal components of intestinal digestion.[288]
[Footnote 288: 'Deut. Chem. Ges. Berg.,' x, 1027-1031.]
Liebig calculated that the daily average amount of fæcal matter passed by a man is 5-1/2 oz; Lawes says that it averages in healthy male adults, 4·2 oz; Parkes estimates it (in Europe) at 4 oz. on the average; Letheby at 2·784, and Frankland at 3 oz. In India, a native on the average excretes as much as 12 oz., this increase over the above quantities being due to the large proportion of rice and farinaceous food of which the Hindoos' diet consists.
The daily average amount of urine excreted by a human being has been given by Lawes at 46 oz.; Parkes places it at 50 oz. by measure for each male adult; Letheby at 31·851, and Frankland at nearly 40 oz. by measure. According to Parkes' figures a population of a thousand persons, would thus void daily 156 lbs. of solids, and 260 gallons of urine; or 25 tons of fæces, and 91,250 gallons of urine per annum; whilst according to Letheby, from the same number of people, the daily discharge would be 2266 lbs. avoirdupois of urine and 177·5 lbs. of fæces.
Messrs Lawes and Gilbert estimate the manurial value of the urine and fæces together at 6s. 8d. per annum for every individual, which corresponds to a yearly produce of about 10 lbs. of ammonia; but Messrs Hoffman, Witt, and Thudichum assess it at 8s. 6d. for a mixed population of both sexes and of all ages, which they say represents about 13 lbs. of ammonia.
Fæcal matter decomposes much more rapidly when mixed with urine than it would otherwise do, ammonia and fetid gases being given off in considerable quantities. Should much water be also present, and the temperature moderately high, light carburetted hydrogen, carbonic anhydride, nitrogen, and sulphuretted hydrogen are likewise evolved.
Unless human excreta be effectually as well as speedily removed from the dwellings, streets, &c., of a community, that community will assuredly pay the penalty of their neglect in the shape of health seriously endangered and deteriorated. If this be so with healthy evacuations, the peril becomes considerably intensified when the excreta are discharged by patients labouring under contagious or many other diseases. See URINE, SEWAGE.
=EX'ERCISE= is essential to the healthy performance of the functions of both body and mind. Without it, the stomach acts feebly, the bowels become inactive, and the circulation of the blood languid and imperfect; the chest contracts, the respiration becomes impeded, the brain is insufficiently supplied with pure arterial blood, the mind grows lethargic, the complexion assumes a sickly and effeminate hue, and the features generally lack the energy and expression which they possess in perfect health. With exercise, the bodily functions are performed with vigour and regularity, the constitution is thereby strengthened, and the attacks of disease repelled. By exercise the mind too is excited to healthy action, its gloomy reveries are dispelled, and the fair face of creation is presented to the mind's eye in its proper hues. It robs undue mental exertion of half its injurious effects upon the body, whilst it stimulates and directs it in its proper course. It improves the temper, and humanises the character. The disposition is refined, the passions restrained, violent emotions checked, the habits improved, and the personal charms promoted under the stimulus of judicious exercise.
To females, bodily exercise is even more necessary than to males. The disposition and education of females are such as tend to produce habits of sloth and indolence to a greater degree than in the other sex. Hence to them exercise is doubly important--it is inseparable from health. The more retiring dispositions of females lead them almost unconsciously into habits of inactivity, which, above all, they should endeavour to shake off and avoid. By so doing--by replacing habits of indolence and inactivity by liveliness and moderate exercise, the development of the body will be promoted, additional grace and elegance imparted to its natural movements, and the enjoyments arising from both mental and bodily health increased, whilst disease and deformity will be prevented by the removal of their cause.
The necessity of exercise exists equally in every grade of society and age of life. Those who are engaged in sedentary employments or in-door occupations, should particularly seek refreshing out-door exercise during the periods of relaxation from their diurnal duties. To the studious and delicate of both sexes, this is absolutely necessary to preserve the health and vigour of the body.
In infancy, exercise of a suitable kind should be almost the constant occupation of the little beings that claim our protection and care. It should, however, be always borne in mind, that the muscular exercise of very young children must be of the gentlest class. Prejudice and ignorance frequently induce nurses and parents to teach their children to walk, as they falsely call it, and thus their feeble limbs are urged to make premature efforts to totter along, before the bones and muscles have acquired sufficient strength to support the body in an erect position. From this course the legs and joints frequently become bent and misshapened, and severe injuries are often inflicted on the head and body by blows and falls. It should never be forgotten, that crawling and rolling are their first modes of progression, and require the least exertion. Next comes the sitting posture; from this the child gradually advances to the erect one; then to walk by slight assistance; and, lastly, to walk safely alone. All this should come naturally, and never be promoted, further than by laying the infant on the carpet or floor, for the full exercise of its little strength. As soon as a healthy child is able to walk instead of crawl, its own disposition induces it to do so. The faculty of imitation, the spirit of enterprise, and the pride of doing what others do, present even in infancy, is rather apt to lead the infant to over-exertion than the contrary. The practice of constantly 'dolling' children in the arms is most prejudicial to the early development of their feeble powers.
It is injudicious to take an infant out during the hottest part of the day in summer; such a proceeding tends to enervate and depress, rather than to strengthen him. Whenever he goes out his head should be protected from the direct rays of the sun by means of a large brimmed hat made of cotton or straw and an umbrella. The neglect of these precautions frequently gives rise to the disordered stomach, sickness, and diarrh[oe]a, so prevalent during very hot weather. During other periods of the day, the weather being favorable and the locality healthy, an infant cannot be too much out of doors, especially during teething.
Infants of three or four months' old may, under certain precautions, be sent out into the open air during the winter. They must be well wrapped up; they should be carried in the nurse's arms, and not consigned to a perambulator; they should never go out in foggy nor wet weather; if the wind be neither in the east nor the north-east there will be no objection to their being sent out on a clear frosty day. Spring is a trying period for infants and children, because of the prevalence of east winds; hence the necessity of seeing that they are well and warmly clad when sent out during this season. There is much less danger of a child taking cold during the autumn than the spring, as in autumn the winds frequently blow from the south, or warm quarter.
In childhood the exercise should be regulated according to constitution and age; avoiding inactivity, on the one hand, and excessive exercise on the other. The out-door plays and pastimes of BOYS will generally be found sufficient, and in some cases will even require to be curbed, to prevent fatigue and the overtasking of the young frame. With girls it is frequently difficult to find sufficient exercise without trespassing on the prejudices of the ignorant, or the routine of their daily education. With them walking, and some healthy amusement, as skipping, hooping, or the like, should be indulged in for some hours daily. When this is impossible or inconvenient, they may be habituated to the practice of the more simply and cleanly portion of the domestic duties. In the performance of the latter, the health will be promoted, whilst the care and attention which is always due by a female to herself and others, at all periods of her life, will become an easy acquisition, and assist the cultivation of the best feelings of her nature.
In youth exercise matures and promotes the development of the frame; and in manhood it is equally necessary, as already noticed, to keep it in healthy action. In age it will be found to assist the vital functions, and put off decay. In fact, to all--young, old, rich, and poor, physical exercise is essential to the permanent enjoyment of health.
In a medical point of view, "exercise, employed moderately, has a tonic and stimulating influence on the system, and is calculated to prove beneficial in a great variety of complaints. Used immoderately, it exhausts both the mental and bodily powers, and produces great debility." (Pereira.) Well-directed exercise favours the preservation of the general health, by calling into direct action the majority of the organs of the body; and it also acts powerfully on the skin, by stimulating its functions, increasing its temperature, awakening its tone, and subjecting it to a current of atmosphere favorable to its respiratory offices. But to be beneficial in the highest degree, exercise must be accompanied by feelings of present interest and enjoyment. The mind must direct and go with it; to ensure its full benefits, the "soul must be present."
"During convalescence, properly regulated exertion is highly serviceable; but it should never be carried so far as to produce exhaustion, and should be pursued for some time in doors, before it be attempted in the open air; the latter, at first, should always take place in a carriage, that can be opened or closed at will; the patient may then attempt short walks in the open air; but, in all cases, it is of importance that he is not unduly fatigued, as, otherwise, injury instead of benefit will be the result. One of the most serious errors, committed with regard to exertion, is that of permitting a convalescent to sit up too frequently, or for too long a time, under the mistaken notion of giving him strength. A patient should never be allowed to sit up longer than is agreeable to his feelings, and never so long as to produce a sense of fatigue." (Dr R. E. Griffith.)
The physiological effects of exercise have been studied by numerous scientific observers. The carefully conducted experiments of Dr Edward Smith have satisfactorily demonstrated that during bodily exertion the circulation of the blood through the lungs is much increased in velocity, that these latter inspire air and eliminate carbonic anhydride in quantities proportionate to the exercise taken, and that these quantities show an enormous increase over the amounts of these gases inhaled and exhaled during a state of rest.
Adopting the recumbent position as unity, Dr Edward Smith has given the following table, illustrating the quantities of air inhaled during various forms of exercise:
Lying position 1· Sitting 1·18 Standing 1·33 Singing 1·26 Walking 1 mile per hour 1·90 Walking 2 miles per hour 2·76 Walking 3 miles per hour 3·22 Walking and carrying 34 lbs. 3·50 Walking and carrying 62 lbs. 3·84 Walking and carrying 118 lbs. 4·75 Walking at 4 miles per hour 5· Walking at 6 miles per hour 7· Riding and trotting 4·05 Swimming 4·33 Treadmill 5·50
Since a man takes into his lungs 480 cubic inches of air per minute, in walking four miles an hour he draws in 2400 cubic inches, and if six miles 3260 cubic inches a minute.[289]
[Footnote 289: Parkes.]
Dr Smith estimated the amount of carbonic anhydride evolved under differing conditions, and found that--
Carbonic acid exhaled per minute in grains. During sleep 4·99 Lying down, and almost asleep (average of three observations) 5·91 Walking at the rate of 2 miles an hour 18·10 Walking at the rate of 3 miles an hour 25·83 Working at the treadmill, ascending at the rate of 26·65 feet per minute (average of three observations) 44·97
The relative amounts of carbonic anhydride eliminated from the lungs during periods of rest and exercise have also been investigated by Pettenkofer and Voit. The following table, which gives the results of their experiments, also records the quantities of oxygen absorbed, and of water and urea excreted at the same time:--
| | Elimination in Grammes of-- | |Absorption|------------------------------| |of Oxygen | | | | | in |Carbonic| Water. | Urea. | |Grammes. | Acid. | | | |-----------------------------------------| Rest-day. | 708·9 | 911·5 | 828·0 | 37·2 | Work-day. | 954·5 | 1284·2 | 2042·1 | 37·0 | | | | | | Excess on | } | | | | work-day | } | | | | (with exception| } 246·6 | 372·7 | 1214·1 | 0·2 | of urea) | } | | | | -----------------------------------------------------------