Metamerism

“ We can state as a First Law [1] of metamerism or somite formation that it is either indefinite in regard to number of metameres or somites produced, or is definite. Animals in the first case we call anomomeristic ”

“ The Third Law of metamerism is that heteromerism may operate in such a way as to produce definite regions of like modification of the somites and their appendages, differing in their modification from that observed in regions before and behind them. ”

“ Especially prominent is the fact that polymerism and metamerism are mainly reserved to the domain of organic chemistry, or the chemistry of carbon, both being discovered there; and, more especially, the phenomenon of metamerism in organic chemistry has largely developed our notions concerning the structure of matter. That this particular feature belongs to carbon compounds is due to a property of carbon which characterizes the whole of organic chemistry, i.e. ”

“ In my opinion the progress of chemistry, especially with regard to solutions, should make rapid strides when the cause of the isomerism of solutions, for instance, of ortho- and pyrophosphoric acids, has become as clear to us as the cause of many well-studied instances of the isomerism, polymerism, and metamerism of organic compounds. ”

“ Isomerism.—Certain investigations on isomerism which have become especially prominent in recent times bear on the possibility of the mutual transformation of isomers. As soon as this reversibility is introduced, general laws related to thermodynamics are applicable (see Chemical Action; Energetics) . These laws have the advantage of being applicable to the mutual transformations of isomers, whatever be the nature of the deeper origin, and so bring polymerism, metamerism and polymorphism together. ”

“ A form which is primitive on the whole may show a more advanced stage of evolution in some particular system of organs than another animal which is on the whole more highly developed and specialized. Thus the independent metamerism of certain organs in the Chitons is not primitive but acquired within the group: e.g. the shell valves and the ctenidia. ”

“ The Fifth Law, relating also to the independence of the meromes as compared with the whole somite, is the law of autorhythmus of the meromes. Metamerism does not always manifest itself in the formation of complete new segments; but one merome may be repeated so as to suggest several metameres, whilst the remaining meromes are, so to speak, out of harmony with it and exhibit no repetition. Thus in the hinder somites of the body of Apus the Crustacean we find a series of segments corresponding apparently each to a complete single somite ”

“ In the simplest cases there seems to be no separate problem of heredity. When a creeping plant propagates itself by runners, when a Nais or Myrianida breaks up into a series of similar segments, each of which becomes a worm like the parent, we have to do with the general fact that growing organisms tend to display a symmetrical repetition of equivalent parts, and that reproduction by fission is simply a special case of metamerism. ”

“ There are subtle and more subtle differences causing isomerism. In the case of metamerism we can imagine that the atoms are differently linked, say in the case of butylene that the atoms of carbon are joined together as a continuous chain, expressed by —C—C—C—C—, normally as it is called, whereas in isobutylene the fourth atom of carbon is not attached to the third but to the second carbon atom, i.e. ”

“ The last law of metamerism which we shall attempt to formulate here, as the Thirteenth, relates to the fusion or blending of neighbouring somites. Fusion of adjacent somites has often been erroneously interpreted in the study of Arthropoda. There are, in fact, very varying degrees of fusion which need to be carefully distinguished. The following generalization may be formulated. “The homologous meromes of two or more adjacent somites tend to fuse with one another by a blending of their substance. ”

“ Before entering into detail it may be useful to consider the nature of isomerism from a general standpoint. It is probable that the whole phenomenon of isomerism is due to the possibility that compounds or systems which in reality are unstable yet persist, or so slowly change that practically one can speak of their stability; for instance, such systems as explosives and a mixture of hydrogen and oxygen, where the stable form is water, and in which, according to some, a slow but until now undetected change takes place even at ordinary temperatures. ”

“ These diatomic compounds, like their elements, are to a considerable degree characterized by the prevalence among them of allotropism; or, as it is more usually called when displayed by compound bodies—isomerism. Professor Graham finds reason for thinking that a change in atomic arrangements of this nature, takes place in water, at or near the melting point of ice. In the various series of hydro-carbons, differing from each other only in the ratios in which the elements are united, we find not simply isomerism but polymerism occurring to an almost infinite extent. ”

“ The β modification, or metatitanic acid, as it is called, is obtained by hydrolysis of the salts by boiling, or by addition of alkali at 100°, as a fine white precipitate. It is almost insoluble in dilute acids and alkalies, but dissolves in water to a colloidal solution; when heated it does not glow. The β form is also obtained when the metatitanates are treated with water; these compounds hydrolyse very readily, but the precipitated dioxide carries down alkali by adsorption. ”

“ The easy transitions of the ortho-, meta-, and pyrophosphoric acids, by means of the hydrogen of ammonia, into the lower acids, and conversely, tend to complicate the study of this very large class of compounds, and it is rarely that the nature of a product thus obtained can be judged from its composition; and this all the more that instances of isomerism and polymerism, of mixture between water of crystallisation and of constitution, &c., are here possible. Many data are yet needed to enable us to form a true judgment as to the composition and structure of such compounds. ”

“ Cases of isomerism in the restricted sense of the word—that is, when with an identity of composition and of molecular weight, the properties of the substances are different—are very numerous among the hydrocarbons and their derivatives. Such cases are particularly important for the comprehension of molecular structure and they also, like the polymerides, may be predicted from the above-mentioned conceptions, expressing the principles of the structure of the carbon compounds [42] based on the law of substitution. ”

“ The concentration of the solution is increased, the osmotic pressure is raised, and we have a hypertonic centre of diffusion. Every centre of catabolism is therefore a positive pole of diffusion. Similar considerations as to the formation and breaking up of the molecules in anabolism and catabolism apply to polymerization. ”

“ According to it, for example, it is evident that there can be no isomerism in the cases of the saturated hydrocarbons C2H6 and C3H8, because the former is CH4, in which methyl has taken the place of H, and as all the hydrogen atoms of methane must be supposed to have the same relation to the carbon, it is all the same which of them be subjected to the methyl substitution—the resulting product can only be ethane, CH3CH3 ”

“ Acetic acid, for example, boils at a higher temperature than water, and has a higher specific gravity than it, whilst its metameride, methyl formate, is lighter than water, and boils at 30°—that is to say, it evaporates very easily.
Let us now turn to carbon compounds containing two atoms of carbon to the molecule, as in acetic acid, and proceed to evolve them from methane by the principle of substitution. ”

“ Again and again, Boone read the legend on the carton: Mekronal is an unanalyzed catalyst derived from the skeletal structure of the non-carbon chemistry life-form Helgae found on Titan. When injected into the human bloodstream, it enables man to breathe all known atmospheres, regardless of content, without toxic effect. Dosage: One ampule every thirty minutes till three ampules have been injected. Repeat weekly until return to normal oxygen-nitrogen atmosphere. ”

“ According to the monistic hypothesis, every mode of kinesis has its concomitant mode of metakinesis, and when the kinetic manifestations assume the form of the molecular processes in the human brain, the metakinetic manifestations assume the form of human consciousness. I am, therefore, not prepared to accept the horn of Mr. Wallace's dilemma in the form in which he states it. All matter is not conscious, because consciousness is the metakinetic concomitant of a highly specialized order of kinesis. But every kinesis has an associated metakinesis ”

“ That they absorb as well as secrete, and that the whole tentacle may be profoundly affected thereby, are proved by the different effects, in kind and degree, which follow the application of different substances. Drops of rain-water, like single momentary touches of a solid body, produce no effect, as indeed they could be of no advantage; but a little carbonate of ammonia in the water, or an infusion of meat, not only causes inflection, but promptly manifests its action upon the contents of the cells of which the tentacle is constructed. ”

“ In chloroform, again, we have a hydrocarbon radical playing nearly the same part as the radical methyl of methylic alcohol, but with chlorine interposing to modify the simple narcotic action of the radical, and greatly to increase the danger of the compound in its effect on the living body. Physiological research has not yet reached, by vital analysis of action, a perfection of knowledge on the subject now in hand. Such analysis is yet in its early days. At the same time a general line of research has been made out, and some results have been obtained which are of direct practical value. ”

“ The introduction of methyl into the complicated molecule of an alkaloid often gives curious results: thus methyl strychnine and methyl brucine instead of producing tetanus have an action on voluntary muscle like curare. ”

“ If it has been found that the species in question are not reddened by the action of methylated spirit, they should be allowed to remain in this fluid, with a few grains of dissolved corrosive sublimate, for at least a few hours, and then they will dry rapidly without any signs of putrefaction; and even those species that are reddened by spirit may be treated to a shorter immersion in this fluid with advantage. ”

“ The product will appear as in infinite metamorphosis.
(From the stand-point of reflection, as continually on the leap from fluid to solid, without ever reaching, however, the required form.—Organizations that do not live in the grosser element, at least live on the deep ground of the aërial sea—many pass over, by metamorphoses, from one element into another; and what does the animal, whose vital functions almost all consist in contractions, appear to be, other than such a leap?) ”

“ Aggregation is excited by almost all the stimulants which induce movement; such as the glands being touched two or three times, the pressure of minute inorganic particles, the absorption of various fluids, even long immersion in distilled water, exosmose, and heat. Of the many stimulants tried, carbonate of ammonia is the most energetic and acts the quickest: a dose of 1/134400 of a grain (.00048 mg.) given to a single gland suffices to cause in one hour well-marked aggregation in the upper cells of the tentacle. ”

“ Formic acid, for example, has two atoms of hydrogen, one attached to the carbon left from the methane, and the other attached to the oxygen which has entered in the form of hydroxyl, and if one of them be replaced by some substance X it is evident that we shall obtain substances of the same composition, but of different construction, or of different orders of movement among the molecules, and therefore endowed with other properties and reactions. ”

“ As we cannot now lean on the views above stated, it is time to abandon the structural theory. They will all be united in chemical mechanics, and the principle of substitution must be looked on only as a preparation for the coming epoch in chemistry, where such cases as the isomerism of fumaric and maleic acids, when explained dynamically, as proposed by Le Bel and Van't Hoff, may yield points of departure. ”

“ We have pictured to ourselves the molecule of methane: let us do the same with ethane. Imagine two carbon atoms side by side linked together or hand in hand. Each will be using one of its hooks to grasp one hook of its brother atom. Hence each will have three hooks to spare on to which we can hook a hydrogen atom. Thus we get two of carbon and six of hydrogen neatly and prettily linked up together. The atoms form an interesting little pattern and to build up the various paraffin molecules with a pencil and paper has all the attractions of a puzzle or game. ”

“ In attempting to explain these singularities, it seems to me that we must resort to one of two suppositions: we must either conceive that the fluid menstruum during the deposition of any particular and extensive formation, must have contained in different places different chemical ingredients; or we must conclude that the alteration in structure in an individual formation, has not so much been derived from the addition or substraction of certain chemical ingredients as from the proportion in which these ingredients have crystallized. ”