NUTRITION. 



743 



exists in a condition that can rightly be termed 

 organised. Moreover, as it is clear that the 

 gelatinous tissues may be formed at the ex- 

 pense of albumen, we are justified in regard- 

 ing this substance as the common pabulum 

 for all. 



In order to form a definite conception of the 

 nature of the transformations, which this prin- 

 ciple is destined subsequently to undergo, it is 

 important to bear in mind, in (inline, that al- 

 bumen cannot be regarded as possessed of any 

 properties that characterize it as a vital com- 

 pound or, in other words, that essentially 

 distinguish it from compounds of an ordinary 

 chemical nature. In its coagulability by heat 

 or by acids in its combination with alkalies 

 as an acid, or with acids as a base and in the 

 absence of any power cf spontaneously passing 

 into forms more decidedly organic than the 

 granules which are seen when it is made to 

 coagulate slowly it is closely analogous to 

 many substances which belong to the domain 

 of inorganic chemistry. It appears, then, to be 

 totally unpossessed of the property of plasticity ; 

 by which we mean the power of being at once 

 converted into organised tissue : so that any 

 deposit, whether fluid or solid, which mainly 

 consists of albuminous matter, must be regard- 

 ed as aplastic. This is a principle of great 

 importance, as we shall see further on. 



Before albumen is ready to be appropriated 

 by the tissues as the material for their nutri- 

 tion, it must undergo a very important change 

 not so much, however, in its chemical compo- 

 sition, as in the re-arrangement of its particles 

 in a new mode, by which its properties are es- 

 sentially changed. There seems reason to 

 believe that, in the proportions of its ultimate 

 elements, it is identical with the substance 

 termed fibrin, into which it is changed during 

 its passage through the chyliferous and sangui- 

 ferous vessels. [See ALBUMEN and FIBRIN.] 

 But there are such decided and well-marked 

 differences between these two compounds, as 

 indicate that they fulfil entirely different pur- 

 poses in the animal economy ; and that whilst, 

 chemically speaking, they are isomeric, the 

 fibrin is endowed with properties of a distinctly 

 vital character that is, altogether different 

 from any with which mere chemistry brings 

 us acquainted. One of the most obvious mani- 

 festations of this difference is the property 

 which is universally regarded as distinctive of 

 fibrin its tendency to coagulate spontaneously 

 when withdrawn from the living vessels, and to 

 pass into the form of a tissue more or less 

 definitely organised. As will presently be 

 shown, the completeness of this transformation 

 depends upon two circumstances in particu- 

 lar ; the perfect elaboration of the fibrin it- 

 self, and the vitality of the surface upon 

 which the concretion takes place. When the 

 fibrin is highly elaborated, it will coagulate in 

 the form of a definite network of minute fibnllae, 

 even upon a dead surface, as a slip of glass ; 

 this is the case, for instance, with the fibrin of 

 the buffy coat of the blood, or with that of the 

 liquor sanguinis (coagulated lymph,) poured 

 out for the reparation of an injured part. But 



in the ordinary fibrin of the blood, the fibrilla- 

 tion is less distinct, when the concretion takes 

 place upon a dead surface. When it occurs in 

 contact with a living surface, however, the co- 

 agulation takes place more gradually ; and it 

 seems as if the particles, having more time to 

 arrange themselves, become aggregated into 

 more definite forms, so that a more regular 

 tissue is produced just as crystals are most 

 perfectly formed, when the crystalline action 

 takes place slowly. It was formerly imagined, 

 that the muscular tissue is the only one pro- 

 duced at the expense of the fibrin of the blood; 

 the other tissues being formed from its albumen. 

 This, however, is unquestionably erroneous. 

 There is no proof whatever, that albumen, as 

 long as it remains in that condition, ever be- 

 comes organised; whilst, on the other hand, 

 there is abundant evidence that the plasticity 

 of any fluid deposit that is, its capability of 

 being metamorphosed into organised tissue is 

 in direct relation with the quantity of fibrin 

 which it contains. Thus the liquor sanguinis 

 or coagulated lymph, thrown out for the repa- 

 ration of injuries, contains a large amount of 

 fibrin ; and this substance is converted, not at 

 first into muscular fibre, but (whatever may be 

 the tissue to be ultimately produced in its 

 place) into a fibrous network, which fills up the 

 breach, and holds together the surrounding 

 structure. This may be regarded as a simple 

 form of areolar tissue, which gradually be- 

 comes more perfectly organised by the exten- 

 sion of vessels and nerves into its substance, 

 and in which other forms of tissue may subse- 

 quently make their appearance. This process 

 will be more particularly described hereafter; 

 it is at present noticed here, as an illustration 

 of the general fact, that fibrin is to be regarded 

 as the plastic element of the nutritive fluids. 



The change from albumen to fibrin is, there- 

 fore, the first important step in the process of 

 assimilation. It commences in the absorbent 

 system ; for the chyle is usually found to con- 

 tain fibrin, even before it enters the mesenteric 

 glands (as is indicated by its tendency, however 

 feeble, to spontaneous coagulation) ; and after 

 it has passed through them, the quantity of 

 fibrin is considerably increased, so that chyle 

 drawn from the thoracic duct usually coagulates 

 with tolerable firmness. This process of elabora- 

 tion continues in the blood : for the quantity 

 of fibrin it contains is always kept up, in health, 

 to a certain standard, although there must be a 

 continual withdrawal of it for the nutritive pro- 

 cesses, without a corresponding regular supply 

 from the chyle ; and we find it, moreover, un- 

 dergoing a sudden and remarkable increase, 

 under the influence of local agencies. The 

 question naturally suggests itself, therefore 

 what is the cause of this change ? It has been 

 usually attributed to some influence effected 

 upon the albuminous fluid, by the living sur- 

 faces over which it is passing ; and the increase 

 in the amount of fibrin in the chyle, which is 

 specially noticed after its passage through the 

 mesenteric glands, has been thought due to 

 some peculiar action of the blood that may 

 come into relation with it, through the thin walls 



