Domestic Economy, Hygiene, Dietetics. 



AIR. 



The common air is a fluid composed mainly 

 of two gases, in certain proportions ; namely, 

 oxygen as twenty and nitrogen as eighty parts 

 in a hundred, with a very minute addition of 

 carbonic acid gas. Such is air in its pure and 

 right state, and such is the state in which we 

 require it for respiration. When it is loaded 

 with any admixture of a different kind, or its 

 natural proportions are in any way deranged, 

 it cannot be breathed without producing inju- 

 rious results. We also require what is apt to 

 appear a large quantity of this element of 

 healthy existence. The .lungs of a healthy 

 full-grown man will inhale the bulk of twenty 

 cubic inches at every inspiration, and he will 

 use no less than fifty-seven hogsheads in 

 twenty-four hours. 



Now, there are various circumstances which 

 tend to surround us at times with vitiated air, 

 and which must accordingly be guarded 

 against. That first calling for attention is the 

 miasma or noxious quality imparted to the air 

 in certain districts by stagnant water and de- 

 caying vegetable matter. It is now generally 

 acknowledged that this noxious quality is in 

 reality a subtle poison, which acts on the hu- 

 man system through the medium of the lungs, 

 producing fevers and other epidemics. 



Putrid matter of all kinds is another con- 

 spicuous source of noxious effluvia. The filth 

 collected in ill-regulated towns, ill-managed 

 drains, collections of decaying animal sub- 

 stances placed too near or within private dwell- 

 ings, are notable for their effects in vitiating 

 the atmosphere, and generating disease in 

 those exposed to them. In this case, also, it 

 is a poison diffused abroad through the air 

 which acts so injuriously on the human frame. 



The human subject tends to vitiate the 

 atmosphere for itself, by the effect which it 

 produces on the air which it breathes. Our 

 breath, when we draw it in, consists of the in- 

 gredients formerly mentioned ; but it is in a 

 very different state when we part with it. On 

 passing into our lungs the oxygen, forming the 

 lesser ingredient, enters into combination with 

 the carbon of the venous blood (or blood which 

 has already performed its round through the 

 body) ; in this process about two fifths of the 

 oxygen is abstracted and sent into the blood, 

 only the remaining three fifths being expired, 

 along with the nitrogen nearly as it was before. 

 In place of the oxygen consumed, there is ex- 

 pired an equal volume of carbonic acid gas, 

 such gas being a result of the process of com- 



bination just alluded to. Now, carbonic acid 

 gas, in a larger proportion than that in which 

 it is found in the atmosphere, is noxious. The 

 volume of it expired by the lungs, if free to 

 mingle with the air at large, will do no harm ; 

 but, if breathed out into a close room, it will 

 render the air unfit for being again breathed. 

 Suppose an individual to be shut up in an air- 

 tight box : each breath he emits throws a cer- 

 tain quantity of carbonic acid gas into the air 

 filling the box ; the air is thus vitiated, and 

 every successive inspiration is composed of 

 worse and worse materials, till at length the 

 oxygen is so much exhausted that it is insuffi- 

 cient for the support of life. He would then 

 be sensible of a great, difficulty in breathing, 

 and in a little time longer he would die. 



Most rooms in which human beings live are 

 not strictly close. The chimney and the chinks 

 of the doors and windows generally allow of a 

 communication to a certain extent with the 

 outer air, so that it rarely happens that great 

 immediate inconvenience is experienced in 

 ordinary apartments from want of fresh air. 

 But it is at the same time quite certain that, 

 in all ordinary apartments where human beings 

 are assembled, the air unavoidably becomes 

 considerably vitia,ted, for in such a situation 

 there cannot be a sufficiently ready or copious 

 supply of oxygen to make up for that which 

 has been consumed, and the carbonic acid gas 

 will be constantly accumulating. This is par- 

 ticularly the case in bedrooms, and in theaters, 

 churches, and schools. 



Perhaps it is in bedrooms that most harm 

 is done. These are generally smaller than 

 other rooms, and they are usually kept closed 

 during the whole night. The result of sleep- 

 ing in such a room is very injurious. A com- 

 mon fire, from the draught which it produces, 

 is very serviceable in ventilating rooms, but it 

 is at best a defective means of doing so. The 

 draught which it creates generally sweeps 

 along near the floor between the door and the 

 fire, leaving all above the level of the chimney- 

 piece unpurified. Yet scarcely any other ar- 

 rangement is anywhere made for the purpose 

 of changing the air in ordinary rooms. 



FOOD. 



A food is a substance which, when intro- 

 duced into the body, supplies material which 

 renews some structure or maintains some vital 

 process ; and it is distinguished from a medi- 

 cine in that the latter modifies some vital ac- 

 tion, but does not supply the material which 



