a history of science-4-第27章
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e equator or the poles； the temperature of the body in man； and of what are commonly called warm…blooded animals； is invariably the same； yet how different are the circumstances in which they live。
〃The animal body is a heated mass； which bears the same relation to surrounding objects as any other heated mass。 It receives heat when the surrounding objects are hotter； it loses heat when they are colder than itself。 We know that the rapidity of cooling increases with the difference between the heated body and that of the surrounding mediumthat is； the colder the surrounding medium the shorter the time required for the cooling of the heated body。 How unequal； then； must be the loss of heat of a man at Palermo； where the actual temperature is nearly equal to that of the body； and in the polar regions； where the external temperature is from 70 to 90 degrees lower。
〃Yet notwithstanding this extremely unequal loss of heat； experience has shown that the blood of an inhabitant of the arctic circle has a temperature as high as that of the native of the South； who lives in so different a medium。 This fact； when its true significance is perceived； proves that the heat given off to the surrounding medium is restored within the body with great rapidity。 This compensation takes place more rapidly in winter than in summer； at the pole than at the equator。
〃Now in different climates the quantity of oxygen introduced into the system of respiration； as has been already shown； varies according to the temperature of the external air； the quantity of inspired oxygen increases with the loss of heat by external cooling； and the quantity of carbon or hydrogen necessary to combine with this oxygen must be increased in like ratio。 It is evident that the supply of heat lost by cooling is effected by the mutual action of the elements of the food and the inspired oxygen； which combine together。 To make use of a familiar； but not on that account a less just illustration； the animal body acts； in this respect； as a furnace； which we supply with fuel。 It signifies nothing what intermediate forms food may assume； what changes it may undergo in the body； the last change is uniformly the conversion of carbon into carbonic acid and of its hydrogen into water； the unassimilated nitrogen of the food； along with the unburned or unoxidized carbon； is expelled in the excretions。 In order to keep up in a furnace a constant temperature； we must vary the supply of fuel according to the external temperaturethat is； according to the supply of oxygen。
〃In the animal body the food is the fuel； with a proper supply of oxygen we obtain the heat given out during its oxidation or combustion。〃＇3＇
BLOOD CORPUSCLES； MUSCLES； AND GLANDS
Further researches showed that the carriers of oxygen； from the time of its absorption in the lungs till its liberation in the ultimate tissues； are the red corpuscles； whose function had been supposed to be the mechanical one of mixing of the blood。 It transpired that the red corpuscles are composed chiefly of a substance which Kuhne first isolated in crystalline form in 1865； and which was named haemoglobina substance which has a marvellous affinity for oxygen； seizing on it eagerly at the lungs vet giving it up with equal readiness when coursing among the remote cells of the body。 When freighted with oxygen it becomes oxyhaemoglobin and is red in color； when freed from its oxygen it takes a purple hue； hence the widely different appearance of arterial and venous blood； which so puzzled the early physiologists。
This proof of the vitally important role played by the red…blood corpuscles led； naturally； to renewed studies of these infinitesimal bodies。 It was found that they may vary greatly in number at different periods in the life of the same individual； proving that they may be both developed and destroyed in the adult organism。 Indeed； extended observations left no reason to doubt that the process of corpuscle formation and destruction may be a perfectly normal onethat； in short； every red…blood corpuscle runs its course and dies like any more elaborate organism。 They are formed constantly in the red marrow of bones； and are destroyed in the liver； where they contribute to the formation of the coloring matter of the bile。 Whether there are other seats of such manufacture and destruction of the corpuscles is not yet fully determined。 Nor are histologists agreed as to whether the red…blood corpuscles themselves are to be regarded as true cells； or merely as fragments of cells budded out from a true cell for a special purpose； but in either case there is not the slightest doubt that the chief function of the red corpuscle is to carry oxygen。
If the oxygen is taken to the ultimate cells before combining with the combustibles it is to consume； it goes without saying that these combustibles themselves must be carried there also。 Nor could it be in doubt that the chiefest of these ultimate tissues； as regards； quantity of fuel required； are the muscles。 A general and comprehensive view of the organism includes； then； digestive apparatus and lungs as the channels of fuel…supply； blood and lymph channels as the transportation system； and muscle cells； united into muscle fibres； as the consumption furnaces； where fuel is burned and energy transformed and rendered available for the purposes of the organism； supplemented by a set of excretory organs； through which the waste productsthe ashesare eliminated from the system。
But there remain； broadly speaking； two other sets of organs whose size demonstrates their importance in the economy of the organism； yet whose functions are not accounted for in this synopsis。 These are those glandlike organs； such as the spleen； which have no ducts and produce no visible secretions； and the nervous mechanism； whose central organs are the brain and spinal cord。 What offices do these sets of organs perform in the great labor…specializing aggregation of cells which we call a living organism？
As regards the ductless glands； the first clew to their function was given when the great Frenchman Claude Bernard （the man of whom his admirers loved to say； 〃He is not a physiologist merely； he is physiology itself〃） discovered what is spoken of as the glycogenic function of the liver。 The liver itself； indeed； is not a ductless organ； but the quantity of its biliary output seems utterly disproportionate to its enormous size； particularly when it is considered that in the case of the human species the liver contains normally about one…fifth of all the blood in the entire body。 Bernard discovered that the blood undergoes a change of composition in passing through the liver。 The liver cells （the peculiar forms of which had been described by Purkinje； Henle； and Dutrochet about 1838） have the power to convert certain of the substances that come to them into a starchlike compound called glycogen； and to store this substance away till it is needed by the organism。 This capacity of the liver cells is quite independent of the bile…making power of the same cells； hence the discovery of this glycogenic function showed that an organ may have more than one pronounced and important specific function。 But its chief importance was in giving a clew to those intermediate processes between digestion and final assimilation that are now known to be of such vital significance in the economy of the organism。
In the forty odd years that have elapsed since this pioneer observation of Bernard； numerous facts have come to light showing the extreme importance of such intermediate alterations of food…supplies in the blood as that performed by the liver。 It has been shown that the pancreas； the spleen； the thyroid gland； the suprarenal capsules are absolutely essential； each in its own way； to the health of the organism； through metabolic changes which they alone seem capable of performing； and it is suspected that various other tissues； including even the muscles themselves； have somewhat similar metabolic capacities in addition to their recognized functions。 But so extremely intricate is the chemistry of the substances involved that in no single case has the exact nature of the metabolisms wrought by these organs been fully
