ENDOSMOSIS. 



ENTOMOLOGY. 



6-16 



the pores of the septum ; and as fast as that which occupies these 

 pores is removed by diffusion, so fast will it be renewed on the other 

 side, just as oil continues to ascend through the capillary channels 

 in the wick of a lamp, so long as it is being dissipated by the combus- 

 tive process at its summit. In this way then an endosmotic current 

 is produced, the force of which will depend upon the diffusion-powers 

 of the two liquids, and upon the difference of the attractive power 

 which the capillary tubes of the septum have for the two respectively. 

 Thus when a solution of sugar or gum is on one side of the septum, 

 and water on the other, the water is the most readily imbibed ; and 

 consequently the chief mixture and diffusion of the liquids, the one 

 through the other, takes place at the surface of the septum in contact 

 with the more viscid liquid. But at the same time this liquid is 

 tending to diffuse itself through the water which occupies the capillary 

 channels of the septum ; and as it is not repelled by the septum, but 

 is only attracted by it in a less degree than the water, a portion of it 

 finds its way in a direction opposed to the principal current, and 

 diffuses itself through the water on the other side, thus constituting 

 Exosmose. Thus it happens that the direction of the principal 

 current, or Endosmose, will be determined by the attractive power of 

 the septum for one or the other of the liquids ; though the diffusion- 

 power of the liquids through each other will help to determine its 

 force. When alcohol and water, for example, are separated by a 

 septum composed of animal membrane, the endoamotic current will 

 be from the water towards the alcohol, because the former liquid 

 more readily 'weta' the membrane, and consequently tends most 

 strongly to occupy its capillary passages ; but, on the other hand, 

 when the separation is made by a thin lamina of caoutchouc, the 

 endosmotic current is from the alcohol towards the water, because the 

 former is most readily imbibed by the septum. It has further been 

 ascertained by the experiments of Matteucci, that when an organic 

 membrane is employed as a septum, the rapidity of transmission is 

 considerably affected by the direction in which the endosmotic current 

 traverses the membrane. Thus, when the skin of the Torpedo was 

 employed, with a solution of sugar on one side of it and water on the 

 other, although there was always an endosmotic current from the 

 water to the sugar, yet this current was strong enough to raise the 

 interior liquid to 80 when the water was in contact with the inter- 

 nal surface of the membrane, in the same time that was occupied 

 by its rise to 20 when the external surface of the membrane was 

 turned towards the water. Again, when the mucous membrane of 

 the stomach of a dog was used as the septum, and its external (or 

 muscular) surface was placed in contact with alcohol, the passage of 

 water from the other side took place with such rapidity as to raise 

 the liquid in the tube to 130 ; whilst if the internal (or mucous) 

 surface of the membrane were placed in contact with the alcohol, and 

 the muscular surface with water, the current was only sufficient to 

 raise the liquid 6 degrees in the same time ; so that it is evident that 

 the transudation of water takes place much more readily from the 

 mucous lining of the stomach towards the outer side of the viscus 

 than in an opposite direction, in virtue simply of the physical proper- 

 ties of the membrane. In fact, according to Professor Matteucci, the 

 cases are very rare in which, with fresh membranes, Endosmose takes 

 place with equal readiness, whichever of the two sides is exposed to 

 the water. 



" The direction which is most favourable to Endosmose through skins 

 is usually from the internal to the external surface, with the excep- 

 tion of the skin of the frog, in which the endosmotic current, in the 

 single case of water and alcohol, takes place most readily from the 

 external to the internal surface. But when stomachs and urinary 

 bladders are employed, the direction varies much more, according to 

 the nature of the liquids employed. This variation appears to have 

 some relation to the physiological conditions in which these mem- 

 branes are placed in the living animal ; thus, the direction most 

 favourable to Endosmose between water and a saccharine solution, is 

 not the same for the stomach of a ruminant as for that of a carnivo- 

 rous animal : as yet however no positive statement can be made on 

 this subject. When membranes are employed that have been dried 

 or altered by putrefaction, we either do not observe the usual differ- 

 ence arising from the position of the surfaces, or Endosmose no longer 

 takes place ; thus affording another indication that it is to the physical 

 condition of the perfectly-organised membrane that we are to look for 

 many of the peculiarities which are noticeable in the transudation of 

 flujrlx through them. Tlje exosmotic current does not bear any con- 

 stant relation to the endosmotic, as may be easily comprehended from 

 the preceding explanation ; for if the liquids have a strong tendency 

 to mutual diffusion, and the difference in attractive power which the 

 septum has for them respectively is not great, each may find its way 

 towards the other, and a considerable exosmose may ensue, with very 

 little change of level. The amount of the exosmotic as of the endos- 

 motic current, varies with the direction in which it traverses the 

 membrane ; thus, when sugar, albumen, or gum was employed in 

 solution, its transudation towards water took place most readily from 

 the internal towards the external surface of all the skins examined 

 by Matteucci, a fact which is not without its significance, when it is 

 remembered that it is in this direction that the secretion of mucus 

 takes place on the skins nf fishes, frogs, Ac. 



" Applying these considerations to the phenomena of imbibition of 

 HAT. HIST. DIV. YOL. U. 



liquids into the tissues and canals of the living body, we shall have 

 to inquire how far they are capable of being accounted for on physical 

 principles, which have been now brought forward. It has been 

 maintained by some that absorption is a purely vital operation, 

 because it does not occur save during the continuance of life. But 

 this is not true, since imbibition will take place into dead tissues, 

 though more slowly than into some parts when living ; and the differ- 

 ence of rate seems to be fully accounted for by the difference of the 

 condition between a mass of tissue, all whose fluids are stagnant, and 

 another in which an active circulation is taking place. Thus, as 

 Matteucci has shown, if the hind legs of a frog recently killed be 

 immersed for some hours in a solution of ferrocyanide of potassium, 

 it will be found that every part of the viscera is so penetrated with 

 the salt, that by touching it with a glass rod moistened with a solu- 

 tion of chloride of iron, a more or less deep blue stain is the result. 

 Now, the same effect is produced much more speedily in a living 

 frog ; and it is easily proved that the imbibition takes place in the 

 latter ease into the blood-vessels, and that the salt is conveyed to the 

 remoter parts of the body by the circulation, instead of having slowly 

 to make its way by transudation through the tissues, as in the dead 

 animal. But further, not only does the movement of blood in the 

 vessels promote the diffusion of liquid, which has been already 

 observed, it also increases the rapidity of the absorption itself in a 

 very extraordinary degree. Thus, if a membranous tube, such as a 

 piece of small intestine, or of a large vein of an animal, be fixed by 

 one extremity to an opening at the bottom of a vessel filled with 

 water, and have a stop-cock attached at the other extremity, and be 

 then immersed in water ascidulated with sulphuric or hydochloric 

 acid, it will be some time before the acid will penetrate to the interior 

 of the tube, which is distended with water ; but if the stop-cock be 

 opened, and the water be allowed to discharge itself, the presence of 

 the acid will be immediately discovered (by tincture of litmus) in the 

 liquid which flows out, showing that the acid has been assisted in its 

 penetration of the walls of the tube by the current traversing its 

 interior. Thus, the continuance of circulation is obviously one of the 

 most patent of all the conditions of absorption, and the difference in 

 the rate of the process in the dead and living organisms, placed under 

 the same circumstances, may bo accounted for in great part, if not 

 entirely, by the stoppage of the circulation in the former. All the 

 circumstances which are laid down by physiologists as favouring 

 absorption are in strict accordance with the physical principles which 

 have been now explained. These circumstances are 1. The ready 

 miscibility of the liquids to be absorbed with the juices of the body. 

 2. The penetrability of the tissue through which the absorption tabes 

 place. 3. The absence of previous distention in the tissues or canals 

 towards which the flow takes place. 4. The elevation of the tem- 

 perature within certain limits. 5. The vascularity of the tissues, and 

 the rate of movement of the blood through the vessels. And the 

 results of experiments upon recently-dead membranes which retain 

 almost exactly the same physical conditions as those which they 

 possessed during life, but have entirely lost their vital properties, 

 seem most decidedly to indicate that the relative facility with which 

 different substances are absorbed, and the direction most favourable 

 to their passage through the tissues, are determined in great part by 

 the physical relations of those tissues (and of the vessels which 

 traverse them) to the liquid which is seeking to enter them. In this 

 way, then, many of the phenomena of selective absorption are pro- 

 bably to be explained, especially in plants and the lower animals. 

 The special absorbent vessels, however, of Vertebrata, seem to possess 

 properties which can scarcely be thus accounted for." (' Principles of 

 Physiology.') [ABSORPTION ; ABSORBENT VESSELS.] 



ENDYMION, a genus of Plants belonging to the class of Endogens, 

 the order Liliacetf, and the tribe Hemerocallidea;. It has a tubular 

 bell-shaped perianth, composed of six conuivent leaves, with reflexed 

 points combined below. The stamens are inserted below the middle 

 of the perianth ; the filaments decurrent. 



E. nutans, the English Blue-Bell. It is also the Scilla nutam, the 

 Hyacinthui non-scriptu*, and Agraphis nutans of various botanical 

 writers. It has linear leaves, with nodding racemes, the flowers bell- 

 shaped, cylindrical ; the apex of the sepals revolute; the bracts 2. This 

 is a very common plant, flowering in May in the woods and thickets 

 of England. It is also common in France and Belgium. The flower- 

 stalk is about a foot high. The leaves are shorter than the flower- 

 stalk. The flowers are generally blue. A white variety is however 

 occasionally seen. 



ENORAULIS. [ANCHOVY; CLCPEID^.] 



ENGYSTOMA. [AMPHIBIA.] 



ENHALUS, a genus of Plants belonging to the natural order 

 Jlydrocliaridacets, the fruit of which, according to Agardh, is eatable, 

 and the fibres capable of being woven. 



EN HYDRA. [OTTERS.] 



ENNEAOONA. [ACALEPHJJ.] 



ENTALOPHORA. [SERTCI.ARIAM;.] 



ENTEROMORPHA. [ALO<] 



ENTO'BIA, a genus of Fossil Annelida. (Portloclc.) 



ENTOMOCO'NCHUS, a genus of Fossil Crustacea, from the Moun- 

 tain Limestone of Ireland. (M'Coy.) 



ENTOMO'LOGY, that branch of science which treats upon insects. 



2 N 



