Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/21

Rh PHYSIOLOGY 11 principles which had proved so successful in the case of the whole organ. When the improvements in the micro scope opened up a new world to the anatomist, and a wholly fresh mechanical analysis of the structure of living bodies became possible, great hopes were entertained that the old method applied to the new facts would soon solve the riddles of life by showing how the mysterious opera tions of the living substances out of which the grosser organs were built were the outcome of structural arrange ments which had hitherto remained invisible, were in fact the functions of minute component organs. A vision of a grand simplicity of organic nature dawned upon the minds of physiologists. It seemed possible to conceive of all living beings as composed of minute organic units, of units whose different actions resulted from their different structural characters, whose functions were explicable by, and could be deduced from, their anatomical features, such units being built up into a number of gross organs, the functions of each of which could in turn be explained by the direction which its mechanical build gave to the efforts of its constituent units. Such a view seemed to have touched the goal, when, in the first half of this century, the so-called &quot;cell-theory&quot; was enunciated as a physio logical generalization. Long before, in the previous century, the genius of Caspar Wolff had led him to maintain that the bodies of living beings may be regarded as composed of minute constituent units, which, being in early life all alike and put together as an unformed mass, gradually differentiate and are ultimately arranged into the tissues and organs of the adult being. But, though Wolff was not unaware of the physiological bearing of his conception, his mind was chiefly bent towards morphological views, and his cell- theory is essentially a morphological one. The cell-theory, however, which became famous in the third decade of the present century, and to which the twin names of Schwann and Schleiden will always be attached, was essentially a physiological one. The chief interest which these authors felt in the ideas that they put forth centred in the convic tion that the properties of the cell as they described it were the mechanical outcome of its build ; and for a time it seemed possible that all physiological phenomena could be deduced from the functions of cells, the anatomical characters of the various kinds of cells determining in turn their special functions. In the cell -theory the con ception of organs and functions reached its zenith ; but thenceforward its fall, which had been long prepared, was swift and great. Two movements especially hurried on its decline. It had long been a reproach to physiologists that, while to most organ s of the body an appropriate function had been assigned, in respect to certain even conspicuous organs no special use or definite work could be proved to exist. Of these apparently functionless organs the most notorious instance was that of the spleen, a large and important body, whose structure, though intricate, gave no sign of what its labours were, and whose apparent use- lessness was a stumbling-block to the theological specula tions of Paley. While in the case of other organs a definite function could be readily enunciated in a few words, and their existence therefore easily accounted for, the spleen remained an opprobrium, existing, as it appeared to do, without purpose, and therefore without cause. The progress of discovery during the present century, by a cruel blow, instead of pointing out the missing use of the spleen, rudely shook the confidence with which the physiologists concluded that they had solved the riddle of an organ when they had allotted to it a special function. From very old times it had been settled that the function of the liver was to secrete bile ; and the only problems left for inquiry as touching the liver seemed to be those which should show how the minute structure of the organ was adapted for carrying on this work. About the middle of this century, however, the genius of Claude Bernard led him to the discovery that the secretion of bile was by no means the chief labour of the liver. He showed that this great viscus had other work to do than that of secreting bile, had another &quot;function&quot; to perform, but a function which seemed to have no reference whatever to the mechanical arrangements of the organ, which could never have been deduced from any inspection however complete of its structure, even of its most hidden and minute features, and which therefore could not be called a function in the old and proper sense of that word. By a remark able series of experiments, which might have been carried out by one knowing absolutely nothing of the structural arrangements of the liver beyond the fact that blood flowed to it along the portal vein, and from it along the hepatic vein, he proved that the liver, in addition to the task of secreting bile, was during life engaged in carrying on a chemical transformation by means of which it was able to manufacture and store up in its substance a peculiar kind of starch, to which the name of glycogen was given. Bernard himself spoke of this as the glycogenic function of the liver, but he used the word &quot;function&quot; in a broad indefinite sense, simply as work done, and not in the older narrower meaning as work done by an organ structurally adapted to carry on a work which was the inevitable outcome of the form and internal build of the organ. In this glycogenic function organization, save only the arrangements by means of which the blood flows on from the portal to the hepatic channels in close proxi mity to the minute units of the liver-substance, the so-called hepatic cells, appeared to play no part whatever ; it was not a function, and in reference to it the liver was not an organ, in the old senses of the words. This discovery of Bernard s threw a great flash of light into the darkness hitherto hiding the many ties which bound together dis tant and mechanically isolated parts of the animal body. Obviously the liver made this glycogen, not for itself, but for other parts of the body ; it laboured to produce, but they made use of, the precious material, which thus became a bond of union between the two. The glycogenic labours of the simple hepatic substance carried out independently of all intricate structural arrange ments, and existing in addition to the hepatic function of secreting bile, being thus revealed, men began to ask themselves the question, May not something like this be true of other organs to which we have allotted a function and thereupon rested content 1 ? And further, in the cases where we have striven in hope, and yet in vain, to com plete the interpretation of the function of an organ, by finding in the minute microscopic details of its structure the mechanical arrangements which determine its work, may we not have followed throughout a false lead, and sought for organization where organization in our sense of the word does not exist? The answer to this question, and that an affirmative one, was hastened by the collapse of the cell-theory on its physiological side, very soon after it had been distinctly formulated. The &quot;cell,&quot; according to the views of those who first Cell- propounded the cell -theory, consisted essentially of an mem- envelope or &quot;cell-membrane,&quot; of a substance or substances ^^ contained within the cell -membrane, hence called cell- tentS) contents, and of a central body or kernel called the and &quot; nucleus,&quot; differing in nature from the rest of the cell- nucleus, contents. And, when facts were rapidly accumulated, all tending to prove that the several parts of the animal or vegetable body, diverse as they were in appearance and structure, were all built up of cells more or less modified,