May 4, 1883. 



KNO^A;'LEDGE 



261 



nourish the body, passes into the capillnries. The nutritive 

 functions of any part of the Woodtlow has lieen dis- 

 charged when the tissues have received their quantum of 

 blood through the capillary walls. If we trace the blood- 

 How onwards — as we may do when the web of the frog's 

 foot is microscopically viewed — we see that the capillaries 

 gradually tend to become of larger diameter ; and finally, 

 by their union, we discover that the capillaries form i-cin^. 

 The name " vein " is familiar enough in common parlance. 

 We know also, as a matter of everyday knowledge, that 

 the name "vein" is given to the bluish-looking vessels 

 we see in the back of the hand, and still more plainly in 

 the arm itself. For the veins, as a rule, lie near the 

 surface, whilst the arteries are deep-seated. 



If we grasp an object firmly in the hand, and tie a 

 bandage say, in the middle of the arm, we notice that the 

 veins grow larger and more prominent. Why is this ! 

 The reply is evident. We have by our bandage obstructed 

 a flow of V>lood "which is passing tip the arm toivards the 

 heart and /iings. Hence the veins swell on the side of the 

 bandage furthest from the heart. We cannot show experi- 

 mentally in such a simple manner the fact that in the 

 arteries the Mow takes place in the opposite direction, 

 namely, from the heart and lungs to the body. But, if we 

 were to place a ligature round any artery^such as the 

 radial artery, in which the "pulse ' is felt, at the thumb 

 side of the arm, about a couple of inches above the wrist;— 

 we should find the vessel to swell abovfthe ligature, instead 

 of below, as in the case of the vein. In other words, we 

 should then be interrupting a flow of blood, which is 

 passing down the arm, to nourish the hand. 



We learn from these plain facts, that the circulation ef 

 the blood really merits that name. It is an incessant round, 

 from the heart and lungs as pure blood, through the body, 

 and back to the heart and lungs as impure or renous blood. 

 The impurities, or waste matters, -which it has received 

 from the body in its course, are got rid of by lungs, skin, 

 and kidneys, and this latter work constitutes that known 

 as " excretion." The course of the circulation — fully 

 wrought out by the immortal Harvey — is as follows. The 

 heart is two-sided (right and left) ; and each side consists 

 of two compartments — an auricle and a ventricle. The 

 rif/ht side of the heart deals with venous or impure blood 

 alone ; whilst the left side is concerned only with arterial 

 or pure blood. The impure blood is returned by the veins 

 to the right auricle : thence it passes to the right ventricle, 

 which pumps it into the lungs. This is one-half, so to 

 speak, of the circulation. In the lungs the blood is purified. 

 Then it is passed on to the left auricle of the heart ; and 

 thence to the left ventricle, which propels it through the 

 arteries all over the body. No mixture of pure and impure 

 blood, therefore, takes place in the heart ; but in frogs and 

 reptiles such a mixture actually takes place, because in 

 these animals the heart is not completely two-sided, or 

 double, as it is in birds, quadrupeds, and ourselves. 



At Buda-Pesth, the capital of Hungary, the National 

 Theatre is to be lighted by 1,000 Swan lamps. 



In connection with the photo-chemical action of ferric 

 oxalate, Mr. Victor Jodin has observed that when 162-5 

 parts — one equivalent — of perchloride of iron, and sixty- 

 three parts of crystallised oxalic acid, dissolved in a litre 

 of water, are exposed in the sunlight, carbonic acid gas is set 

 free in such quantity as to supply the requirements of 

 plants enclosed in a vessel with it, the absorption and de- 

 composition of carbonic acid by the plant being likewise 

 a photo-chemical action, because it requires sunlight to 

 aid it. 



HOW TO USE OUR EYES.— V. 



By John Bkowninc;, F.R.A.8. 



(Conlinued from p. 194.) 



rpO the precautions we should take with regard to our 

 X own eyes, I must add a few words of w arning respect- 

 ing those of our children. 



Never allow infants to be exposed to the full glai-e of 

 the sun. ^Men shade their eyes with the brims of theii- 

 hats and ladies carry parasols. But infants wear nothing 

 which projects over tlie forehead, and they are constantly 

 to be seen in perambulators with their unprotected faces 

 turned full towards the sun, and I have frequently seen 

 them left by careless people in such a position, with their 

 poor little eyes closed, moving uneasUy about, and unable 

 to find any relief from their sutl'ering. 



It is ditlicult to estimate the amount of mischief which 

 may be done to their eyes by such thoughtless cruelty. 



The generally-received idea is that the spectacles worn 

 should always be the lowest power the wearer can 

 see clearly with, because the eye should have a slight 

 adjustment left to make for itself. This is entirely wrong. 

 The spectacles worn should fully meet the want of adjust- 

 ment or focussing power. 



There should be not oiihj no conscious strain, but I'O ",i- 

 conscious strain, on the part uf the wearer. 



Sometimes, though not very often, persons imagine that 

 because they have reached a certain age they must require 

 spectacles. I recollect one instance of this kind. A well- 

 known admiral came to nie and told me that he had never 

 worn spectacles, but he was quite sure he required them. 



I gave him a book of test-types, and asked him to tel! 

 me the smallest size type he could read, and at what dis- 

 tance from the eye he could read it. Having obtained 

 this information, I gave him a pair of very low power 

 spectacles, suitable for a long-sighted person, and then, 

 directly afterwards, a pair suited for a short-sighted person. 

 He said he could see equally well with either. This \vas 

 just what I expected. 



"Now," said I, "here is a pair of spectacles that will suit 

 you." He put them on, and, taking up the book, he said : "Oh, 

 yes, I can see better with these than either of the others." 

 "I thought you would," was my reply, "because if you 

 take them off you will find that they are a pair of spec- 

 tacle frames — there are no glasses in them ! " 



Had this gentleman gone to a quack, he would certainly 

 have given him spectacles several years before he required 

 them. 



I only wish to say one sentence more on this subject : 

 Do not believe that any loudly puffed spectacles can be 

 of special service to you. There is skill, of course, required 

 in making good lenses of tine optical glass or Brazilian 

 pebbles, but there is still more skill required in suiting the 

 spectacles to each particular person's requirements. 



How can this skill, only to be acquired by knowledge, 

 combined with practice, be possessed by every watchmaker, 

 chemist, jeweller, or ironmonger, who buys a dozen pairs 

 of spectacles and writes up that he is a practical optician 'f 

 Remember that a pair of spectacles which would exactly 

 suit one person would, in a short time, almost blind 

 another ! 



I doubt if more than one person out of each dozen 

 receives the full benefit from s-pectacles they should do, 

 while there are four out of each dozen injure their eye- 

 sight by using spectacles unsuited to them. 



Year after year I have been pained by people living in 

 the country coming to me for spectacles, when their eye- 

 sight had been first injured by using improper lenses. 



