581 



RESPIRATION. 



RESPIRATION-. 



692 



place either out of the structure of organic beings, or in their 

 interior. The carbonic acid given off from food in the stomach or 

 intestines ought not most assuredly to be regarded as the result of 

 respiration, yet this would be the case if we accepted a mere chemical 

 definition of respiration. 



Respiration then appears to be a purely animal process, by which 

 the fluids of the animal are brought into contact with the oxygen of 

 the air, the final result of which is the discharge of carbonic acid gas. 

 This process is continuous in the animal kingdom ; and in the great 

 majority of cases in the higher animals, if it be suspended for a few 

 minutes the animal dies. When an animal dies from being deprived 

 of oxygen gas, it is said to be suffocated. 



In the higher animals special organs ara provided for the perform- 

 ance of that portion of this function which consists in the taking up 

 of oxygen gas directly from the atmosphere, and allowing the carbonic 

 acid to escape. Hence these arrangements have been called Organs of 

 Respiration. It should however be understood that the chemical 

 changes involved in the disappearance of the oxygen, and the appear- 

 ance of the carbonic acid, are carried on in the tissues themselves. 

 The lungs, gills, or sacs, are organs where the blood receives the 

 oxygen gas, and gets rid of its carbonic acid ; whilst the capillaries 

 of the systemic circulation are the organs by which the blood gets rid 

 of its oxygen, and the tissues their carbonic acid. TThe process of 

 respiration then is the same in the highest as in the lowest animals, 

 with this exception, that in the lowest animals there are no organs of 

 circulation, and no organs of ventilation, as the lungs and gills may 

 be called, for conveying the oxygen and carbonic acid to and from 

 the tissues. 



The absorption of oxygen by the animal cell seems to effect three 

 great objects : 1. The preparation of the materials taken up as food 

 for the purposes of nutrition. 2. The removal of certain constituents 

 which have been employed in nutrition, and destroyed during the 

 performance of the function of the part. 3. The production of heat, 

 arrangements for the accumulation of which are made in the higher 

 animals, which are from this circumstance called warm-blooded. 

 [HEAT, ANIMAL.] 



That the performance of one or other of these functions is essential 

 to the life of animals is seen from the fact that, should the supply of 

 oxygen to the tissues of animals be limited or suspended, they exhibit 

 deficient vitality or die. It is not only one function of the animal 

 body that is affected by this deprivation, but all ; so that we find the 

 amount of oxidation performed by this process becomes the exponent 

 of the amount of vital activity displayed by any particular animal, or 

 class of animals. When the functional activity of an animal is great 

 it consumes more oxygen, and gives off more carbonic acid, than 

 when it is small. Thus, in animals which hybernate, the amount 

 of oxygen consumed, and carbonic acid given out, is much less 

 during their period of repose than during their period of activity. 

 Sluggish and slow-moving animals consume less oxygen than those 

 which are active. Thus the Mollusca consume less oxygen than 

 the various tribes of active insects. It is also found that animals 

 whose movements are slow will support the absence of oxygen 

 gas for a very much longer time than those whose movements are 

 quick. 



Under the head of the various articles devoted to the classes and 

 families of animals some account is given of the general character and 

 structure of what are called the Respiratory Organs. In the lowest 

 forms of animal*, the Infusoria, the whole surface of the animal is 

 exposed to the fluid in which they live, and which contains the 

 oxygen necessary to produce the respiratory changes. When a number 

 of cells are congregated together, as in the sponges, and cavities or 

 tubes are formed, special provision is made by means of cilia, or mole- 

 cular movements, for carrying the fluid into these cavities, or tubes, 

 as seen in many of the polygastric animalcules and the sponges. 

 Passing higher in the forms of radiate animals, as in the Polypifera, 

 we find the arrangements for introducing water into the interior of 

 the animal becoming more complicated, till in the Jfololhuriailir, we 

 find a special system of vessels for supplying this fluid, which have 

 been called an ' aquiferous,' or ' water vascular system,' and which 

 becomes more fully developed in the Entozoa, the lowest tribe of the 

 Articulata. 



These arrangements amongst the lower animals are preparatory to 

 the two predominant forms of respiratory apparatus which are found 

 in the higher animals. The provision for supplying the system with 

 oxygen is in them made by means of a fluid called blood, and which in 

 carried by a circulating apparatus to all parts of the body. [BLOOD ; 

 HEART.] This circulating apparatus brings the blood in contact with 

 the air by one of two arrangements. Either the aerating organ is a 

 projection from the surface of the body, when it is called a Gill ; or 

 it U a depression in the surface, when it is called a Sac or Lung. The 

 first of these arrangements is found in all animals which breathe 

 through the agency of water, whilst the second is found in those which 

 breathe air. [LuNOS.] In the Aquatic Moiluica, the Cirripedia, the 

 Annelida, the Cruitacta, the aquatic larvre of insects, the fishes, the tad- 

 pole condition of the Anififtibia, and the perennibranchiate forms ol 

 that family, we meet with a vast variety of forms of gills adapting 

 these animals to lead an aquatic existence. On the other hand, we 

 find in the Terrestrial Moliutca and the Insects the simplest forms 



of air-breathiug apparatus; whilst in the Reptiles, the Birds, and 

 Mammalia, we have varied forms of lungs. 



Man breathes by means of lungs. The structure and arrangement 

 of those organs, and the nature of the movements performed by the 

 muscles which contribute to the performance of their peculiar func- 

 tion, are described under the article LUNGS. The lungs of man are so 

 constructed that they are alternately expanded and contracted. 

 During each expansion, a certain quantity of air is taken into the 

 lungs, and this act is called Inspiration. This expansion is followed 

 by a corresponding collapse, during which the lungs occupy a smaller 

 space, and a certain quantity of air is expelled this is called 

 Expiration. The quantity of air changed in the human lungs at 

 each respiratory effort varies. It is however easily measured by 

 blowing into a vessel filled with water or ether fluid, when the 

 amount of fluid displaced will be the measure of the quantity of air 

 thrown out from the lungs. Instruments of this kind, with an iudex 

 attached, under the name of Spirometers, are now frequently 

 employed as a means of diagnosis in diseases of the chest. The 

 difficulty however of securing freedom from disturbing causes renders 

 their results less to be depended on than could be wished. The quantity 

 of air thrown out from the lungs has been variously estimated, but 

 probably from 20 to 25 cubic inches is near the truth. Scharling con- 

 ducted a series of experiments on the quantity of carbonic acid 

 thrown out of the lungs by persons of different sexes and various 

 ages. The following table gives an idea of the average relations of the 

 excretion of carbonic acid gas during one hour : 



The air that is habitually and almost uniformly changed in breathing 

 is by Mr. Hutchinson called Breathing Air. " The quantity over and 

 above this which a man can draw into the lungs in the deepest inspi- 

 ration he names Complemental Air ; its amount is various, as will be 

 presently shown. After ordinary expiration, such as that which 

 expels the breathing air, a certain quantity of air remains in the 

 lungs, which may be expelled by a forcible and deeper expiration : 

 this he terms Reserve Air. But even after the most violent expiratory 

 effort the lungs are not completely emptied ; a certain quantity always 

 remains in them, over which there is no voluntary control, and which 

 may be called Residual Air. Its amount depends in great measure on 

 the absolute size of the chest, and has been variously estimated at 

 from 40 to 260 cubic inches. 



" The greatest respiratory capacity of the chest is indicated by the 

 quantity of air which a person can expel from his lungs by a forcible 

 expiration after the deepest inspiration that he can make. Mr. 

 Hutchinson names this the Vital Capacity : it expresses the power 

 which a person has of breathing in the emergencies of active exercise, 

 violence, and disease; and in healthy men it varies according to 

 stature, weight, and age. 



" It is found by Mr. Hutchinson, from whom nearly all our in- 

 formation on this subject is derived, that at a temperature of 

 60" Fahr., 225 cubic inches is the average vital capacity of a healthy 

 person 5 feet 7 inches in height. For every inch of height above this 

 standard the capacity is increased on an average by 8 cubic inches ; 

 and for every inch below it is diminished to the same amount. This 

 relation of capacity to height is quite independent of the absolute 

 capacity of the cavity of the chest; for the cubic contents of the 

 chest do not always or even generally increase with the stature of the 

 body, and a person of small absolute capacity of chest may have a 

 large capacity of respiration, and vice versa. The capacity of respi- 

 ration is determined only by the mobility of the walls of the cheat ; 

 but why this mobility should increase in a definite ratio with the 

 height of the body is yet unexplained, and must be difficult of 

 solution, seeing that the height of the body is chiefly determined by 

 that of the legs, and not by that of the trunk or the depth of the 

 chest. But the vast number of observations made by Mr. Hutchinson 

 leave no doubt of the fact as stated above. 



" The influence of weight on the capacity of respiration is less 

 manifest and considerable than that of height ; nnd it is difficult to 

 arrive at any definite conclusions on this point, because the natural 

 average weight of a healthy man in relation to stature has not yet 

 been determined. As a general statement however, it may be said 



* The kilogramme=2-205 lb. very nearly. The gramme=16-4M grains. 



