March 23, 1882.] 



KNOWLEDGE ♦ 



179 



food, when bile from the liver is also poiired upon it In 

 the sweetbread's secretion we find water, minerals, and a 

 substance called pancreatin. Starch is certainly acted 

 upon by this substance, and such starchy foods as may 

 have escaped digestion in the mouth, are changed into 

 dextrin and grape sugar after leaving the stomach. The 

 sweetbread's "juice" also assists in the digtstion of fats, 

 and must in this way aid bile in its work ; whilst it is also 

 believed to possess some action upon the albuminous parts 

 of the food, an eQect accessory to that produced by the 

 gastric juice of the stomach. 



When the food is passing along the tube which succeeds 

 the stomach, and which is called the intestine (or bowel), 

 it is thus nii.\ed with bile and pancreatic juice. These 

 fluids are poured upon the food in the first part of the 

 intestine. In total length, the intestine in man measures 

 -6 ft. ; the small intestine making up I'n ft. of this length, 

 and the large intestine about Gft. As the food travels 

 along the small intestine, it has also poured upon it the 

 fluids furnished by the glands of the bowel. The glands 

 are of various kinds, and some at least appear to exercise 

 a digestive action on the food. 



To sum up our notes on digestion, then, we discover 

 that the food is attacked, so to speak, at various stages of 

 its progress along the digestive tube by the fluids or 

 " secretions " that are poured upon it ; that, secondly, 

 these secretions exert each a chemical action on the food ; 

 thirdly, that their effect is to convert the food into a milk- 

 like fluid (called chyle) which contains the concentrated 

 nourishment of the food, and which will bo added in due 

 course to the blood ; and, lastly, that the fluids which thus 

 accomplish digestion are provided each by an organ or 

 organs called, generally, glands. That which remains for 

 us is to inquire, how or by what means the glands produce 

 and manufacture the secretions of which we have just 

 spoken. 



In a manufactory there are three chief elements which 

 demand consideration at the bands of the economist The 

 first is the raw material, the second is the workman or 

 workmen, and the third is the manufactured article. Each 

 " gland " in a human body is a manufactory which turns 

 out a manufactured article (bile, gastric juice, saliva, kc.) 

 from raw material. The raw material in the physiological 

 factories is blood. Here, however, we come face to face 

 with a very deep physiological problem. From one and 

 the same raw material — blood — which is supplied to the 

 *' glands," each factory produces a special product, diftering 

 widely from that of other "glands." Bile and pancreatic 

 juice, the " tears " of the eyes, the mucous secretion of the 

 nose, and the saliva, are widely different glands ; yet they 

 Are manufactured from the same raw material. But what 

 of the workmen which perform the work ? Here we come 

 lace to face with the microscopic elements of our bodies 

 known as cdls. In our last paper I spoke of jyrotophtsm, 

 the "physical basis of life," as seen in the Atnuba, or 

 "Proteus-animalcule." Xow the cells of our bodies, when 

 in an active, living state, consist of protoplasm. The liver 

 18, practically, an agglomeration of hepatic cells, each about 

 the Yo'o_th of an inch in diameter. It is " cells " of 

 other kinds that make up the essential parts of the salivary 

 glands; it is " cells " that compose the secreting part of 

 the sweetbread ; it is " cells" that make the gastric j\iice 

 in the glands of the stomach. If, as is certainly the case, 

 the cell is a mass of living " protoplasm," then it is 

 clear that we have at last tracked the problem of 

 secretion as far as we may. Supply a liver cell with 

 blood, and it makes bile ; supply a cell of the stomach's 

 glands with blood, and it makes or "secretes" gastric 

 juice. The " properties of protoplasm " is a phrase that 



means much or little, according as we are wise or heedless 

 of life's acts and wonders. He who is heedless will l>e 

 apt to say there is no mystery after all ; he will urge 

 that living protoplasm, because it lives, discharges these 

 functions, and that there is an end of the matter. 

 But he who is wise will not rest here. He will 

 seek to know n-li;/ one bit of protoplasm makes 

 bile, and ir/iif another makes saliva. lie will regard 

 with wonder the fact that all forms of protoplasm appear 

 essentially similar to all scientific tests. He will look 

 below the surface, and see in the adaptations of this one 

 substance to many and varied ends, another ]iroof of the 

 great contention of modern science — that, after all, the 

 evolution of life's ways and works is as discernible in a 

 study of " secretion," and " cells," as in the growth of the 

 complex animal from the simple egg, or of the flower and 

 its variety from the primitive germ that precedes fruition. 



SAXD-DUNES. 



THE subject of sand-dunes having been referred to in a 

 recent number of Knowledce, the following facts 

 relating to them may prove of interest : — 



Sand-dunes travel in the direction of the prevalent wind. 

 They continue to advance inland and overwhelm every- 

 thing on their march, even streams failing to arrest their 

 progress. 



"The mouth of the river Adour, on the west coast of 

 France, has been shifted two and a half miles from its 

 original position by encroaching sand-dunes. 



Along the French coast, where they extend for miles, 

 they average from 50 ft to GO ft in height, while on the 

 coast of Holland they have been met with as high as 

 260 ft 



On the shores of the Bay of Biscay they travel inland 

 at a rate of about 16 ft in a year, while in some parts of 

 Denmark the rate of encroachment reaches 24 ft. in the 

 same time. 



The advance of these dunes has been very much checked 

 within the last few years by their having been planted with 

 the cluster-pine, sand marram (Antudo arennrin), etc. These 

 plants bind the sand and form a covering and a net-work 

 of rootlets. 



Before these precautions were taken, houses, fields, and 

 even whole parishes were buried beneath the sand. 



Occasionally these planted dimes become covered, the 

 vegetation then decomposes and forms a layer of peaty 

 matter. 



In Cornwall, the West Indies, and other places where 

 the Eund is calcareous, or formed of comminuted shells, 

 etc., it is compacted into a hard stone by the action of 

 rain-water percolating, dissolving the carbonate of lime, 

 and re-arranging it as a cement ; this rock is common in 

 the Bahamas and Bermudas, where it weathers into caves 

 and picturescjue crags. 



In Cornwall the hardest granite may be seen polished 

 and woni into furrows where blown sand has come in 

 contact with it, and I believe the Egj-ptian monuments 

 exposed to the sand drifting from the Libyan desert pre- 

 sent a similar polished appearance. Advantage is taken 

 of the polishing or wearing property of blown sand, as in 

 the case of the artificial sand-blast used for engraving 

 glass, or cleaning files, A'c. 



Has "Philalethes" heard of the "musical" sands'! 

 There are some on the coast of Skye : as one walks over 

 them they give out a musical note, probably due to the 

 sand-grains being of equal size. 



C. C.\Ris Wilson, F.G.S. 



