COURSE OF ABSORBED MATERIAL.

109

itself. The double condition here specified must be complied with; the material to be introduced must be dissolved in water, and must be soluble in the blood. If the latter condition be wanting, the vessels seem to manifest a selecting power, absorption not taking place, as in the case of litmus, presented above as an illustration—a coloring matter which, though soluble in water, is not soluble in alcohol, and so can not, under those circumstances, pass through a piece of bladder.

While thus there is an introduction of digested material from the stomach and intestine into the blood, the physical principles which are guiding us in our explanation teach us that there must be a percolation of the more watery portions of the blood in the opposite direction-that is, into the digestive cavity. There is every reason to believe that this percolation is to a far greater amount than is generally supposed. Under certain circumstances, it is a matter of ordinary observation that the water discharged from the intestine is more in quantity than that which has been taken as drink.

absorbed mate

rial to the liv

er; modifica

goes.

Turning our attention now to the course which is followed by the liquid which has been introduced from the digestive cavity Course of the into the blood-vessels, we must bear in mind that the content of those vessels is composed of two distinct portions, the matter thus recently introduced, and the original venous tions it underblood. These together make their way through the portal vein to the liver, a gland of double function, and, as we may say in this respect, of double structure; for, though it has a duct for the disposal of the products which arise from its action on one portion of the material thus brought to it, the venous blood, it is ductless as regards the other portion, which has been received from the digestive cavity. This portion, under the influence of the cell structure of the liver, undergoes profound modification; for instance, liver-sugar makes its appearance, though none existed before. It is not necessary for us to specify these changes particularly here, since we shall have to examine them more in detail in a subsequent chapter; but it may be observed that the anatomical peculiarity of the liver in this branch of its duty is, that it simply impresses a change on the compounds thus brought to it, gives rise to no excretions, and therefore has no channel or duct of escape, unless indeed we say, as we are actually justified in doing, that the hepatic veins themselves are the ducts of the liver in this respect.

Though it does not strictly appertain to the subject of which we are now speaking, absorption, we may, for the sake of completeness, describe, in a superficial manner, what occurs to the other constituent of the portal blood, its proper venous portion. This, brought into the liver, is acted upon by that organ and decomposed into two portions, one of which, constituting the bile, is brought back eventually through the proper bile duct

110

Return of a

SUMMARY OF ABSORPTION.

into the intestine. The other is carried into the blood circulation. I believe that this separation is of a purely physical kind, and is accomplished by mere filtration, the elements of the bile all pre-existing in the blood. However that may be, the separation in a chemical sense is very distinct, for the nitrogenized ingredients are saved to the system, and carried into the general circulation through the hepatic veins; but the biliary material brought back into the intestine is a hydrocarbon tinctured part to the with a little coloring matter, which, being on a rapid career of intestine. retrograde metamorphosis, is prone to act as a ferment, and therefore unfit to remain in the system; accordingly, it is removed with the excrement. The other portion, the hydrocarbon, which has been brought into the intestine, is not yet done with; advantageous use can still be made of it. It can aid in the introduction of fats through the villi into the lacteals, and, from its combustible nature, is of an equal value to the system with the oils it thus helps to introduce. We may advantageously trace the course which it follows, for in so doing we shall complete our description of the function of absorption in its most general

sense.

the villi.

The fat matters which have been subdivided into portions of microManner of scopical minuteness, small globules, each of which is coated action of over with a delicate film of albumen, and all brought therefore into the state of an emulsion, can make their way by reason of the peculiar properties of the investiture which thus covers them through the pores of the villi into the lacteal. For my own part, I do not believe that there is any passage through the epithelial cells, but that it is entirely interstitial, and that it is not unlikely that the biliary constituent aids in this progress. It signifies nothing that the spaces through which the fat globules have to go are less than their own diameter; they can elongate into worm-like forms, just as, under the same circumstances, blood-cells can do, and, the moment they reach the cavity of the lacteal, reassume their sphericity by reason of their cohesion. The albumen that now accompanies them in the liquid form, as the other chief ingredient of the chyle, comes, for the most part, from the blood-vessels of the villi. The chyle moves onward to the mesenteric glands, and makes its passage through them either in naked tubes or through their pulpy structure, is submitted to cell action and to arterial blood, undergoes the morphological changes which have been described in the preceding chapter, and, gaining the thoracic duct, is brought into the general circulation.

In the description here offered of the function of absorption, the agency of physical forces alone has been considered, and these I conceive to be abundantly sufficient to enable us to account for all the phenomena.

The Offices and Relation of Blood in the System.-The Plasma and Cells.-General Properties and Composition of the Blood.—Quantity in the Body.—Coagulation.-Blood-cells.—Their successive Forms.-The perfect Cell.-Hæmatin: its Properties.-Number of Blood-cells.—Plasma: its Composition, and Variations of its Ingredients.—Albumen, Fibrin, Fat, Sugar.—Mineral Ingredients of the Cells and Plasma compared.-Gases of the Blood.-Changes occurring during the Circulation.-General Functions of the different Ingredients of the Blood.-Introduction of Oxygen by the Cells.-Their transient Duration.

Ir is necessary for the functional activity of every organized being that there shall circulate through all parts of it a nutritive liquid. In plants, it is the sap; in animals, the blood.

Since the life of plants manifests itself, for the most part, in a purely formative result, and involves little or no destruction of parts, The blood: its the circulating current is devoted almost entirely to nutrition. functions. But in animals, whose conditions of existence involve extensive and unceasing destruction, the current is burdened with another duty. It is also the means of removal of dying or wasted portions.

and removal of

In the first chapter it was shown that about a ton and a half of material is required by a man in the course of a year, and that in Introduction the same period a like amount is removed from the system. material by the When we reflect that the introduction and removal of this blood. immense mass is accomplished through the agency of the circulating blood, it is obvious that that fluid must be undergoing the most rapid changes. The rapidity with which dying matters are removed is strikingly illustrated by the minute extent to which they are permitted to accumulate in a healthy state. These elements of decay are strained off or exhaled as quickly as they arise. That fancied power, the "vis medicatrix naturæ," is only an ideal expression of the perfection with which the various eliminating mechanisms work. Poisonous agents, whether they have been introduced from without or have originated from morbid actions within, like all other useless or noxious products, find their proper channel of escape, and the system will thus rid itself of intoxicating liquids and narcotic drugs if their quantity does not exceed the amount that it can destroy or excrete in a special period of time.

Considered in its relation to nutrition, the circulating liquid presents many interesting aspects. Each of the thousand variously-constituted parts of the body is withdrawing the supplies it needs: the muscular, the

112

Interconnec

tion of all parts through this circulation.

PROPERTIES OF THE BLOOD.

nervous, the cartilaginous, the bony; and hence there arises. a general balance in the system, each part making its demand at a certain rate, and each observing a complementary action to all the rest. Many of those phenomena which, in the infancy of physiology, were regarded as instances of sympathy between different parts, are clearly dependent on these conditions; for the development of one part, by abstracting special material from the circulating liquid, permits the co-ordinate development of another, or perhaps puts a stop to it. The minutest portion of the mechanism is thus indissolubly connected with all the rest through the medium of the blood.

Seen as it circulates in the vessels, the blood consists of a colorless The plasma liquid containing corpuscles. In man, some of these corpuscles and cells. are white and others red. To the liquid in which they float, the designation of the plasma is given; the colored corpuscles, from their Properties of shape, are called discs or cells. The specific gravity of the the blood. blood varies from 1.050 to 1.059, the variation being, to a considerable extent, due to variations in the quantity of the cells. The temperature is about 100° Fahr., the reaction always alkaline; there is also a faint sickly odor, which differs in different animals. The capacity of blood for heat is in direct proportion to its density. The cells give to the blood its tint of color, and this, in the systemic arteries, is crimson, in the veins, deep blue. However, the color of arterial blood depends considerably on the condition of respiration. An imperfect introduction of oxygen, as in hot climates, causes the arterial blood to assume a dark color, and the same is observed when chloroform, ether, or diluted irrespirable gases are breathed. The blood of the male sex is heavier than that of

This table leads to the hypothetical formula of the ultimate constitution of blood:

C48 H39 No O15

6

As to the quantity of blood in the circulation, it has been variously estimated. It may perhaps be taken at one eighth of the weight Quantity of of the body, a number which is agreed upon by several authors, blood in the body. and in support of which Lehmann mentions the following interesting observation: "My friend, E. Weber, determined, with my cooperation, the weights of two criminals before and after decapitation. The quantity of blood which escaped from the body was determined in the following manner: Water was injected into the vessels of the trunk and head until the fluid escaping from the veins had only a pale red or yellow color. The quantity of blood remaining in the body was then calculated by instituting a comparison between the solid residue of this pale red aqueous fluid and that of the blood which first escaped. By way of illustration, I subjoin the results yielded by one of the experiments. The living body of one of the criminals weighed 60,140 grammes; and the same body, after the decapitation, 54,600 grammes; consequently, 5540 grammes of blood had escaped. 28.560 grammes of this blood yielded 5.36 grammes of solid residue; 60.5 grammes of sanguineous water collected after the injection contained 3.724 grammes of solid substances. 6050 grammes

of the sanguineous water that returned from the veins were collected, and these contained 37.24 grammes of solid residue, which corresponds to 1980 grammes of blood; consequently, the body contained 7520 grammes of blood (5540 escaping in the act of decapitation, and 1980 remaining in the body); hence the weight of the whole blood was to that of the body nearly in the ratio of one to eight. The other experiment yielded a precisely similar result."

A short time after it has been drawn, the blood undergoes coagulation, and is then said to be composed of the serum and the clot. Spontaneous In this state it is sometimes spoken of as dead. The plasma of living blood differs from the serum of dead in containing clot. fibrin.

division into serum and

The coagulation of the blood commences within about ten minutes after it has been drawn, and the clot undergoes a subsequent The coagulacondensation during one or two days. To understand the tion of blood. physical nature of this singular change, we may conveniently regard the

H