Thomas Henry Huxley and Peter Chalmers Mitchell

“ No forms of matter which are either not living, or have not been derived from living matter, exhibit these three properties, nor any approach to the remarkable phenomena defined under the second and third heads. But in addition to these distinctive characters, living matter has some other peculiarities, the chief of which are the dependence of all its activities upon moisture and upon heat, within a limited range of temperature, and the fact that it usually possesses a certain structure or organization. ”

“ The biological sciences are those which deal with the phenomena manifested by living matter; and though it is customary and convenient to group apart such of these phenomena as are termed mental, and such of them as are exhibited by men in society, under the heads of psychology and sociology, yet it must be allowed that no natural boundary separates the subject matter of the latter sciences from that of biology. Psychology is inseparably linked with physiology ”

“ The broad distinctions which, as a matter of fact, exist between every known form of living substance and every other component of the material world, justify the separation of the biological sciences from all others. ”

“ Recent investigations point to the conclusion that the immediate cause of the arrest of vitality, in the first place, and of its destruction, in the second, is the coagulation of certain substances in the protoplasm, and that the latter contains various coagulable matters, which solidify at different temperatures. And it remains to be seen, how far the death of any form of living matter, at a given temperature, depends on the destruction of its fundamental substance at that heat, and how far death is brought about by the coagulation of merely accessory compounds. ”

“ If the processes of disintegration and of reconstruction which characterize life balance one another, the size of the mass of living matter remains stationary, while, if the reconstructive process is the more rapid, the living body grows. ”

“ A process of waste resulting from the decomposition of the molecules of the protoplasm, in virtue of which they break up into more highly oxidated products, which cease to form any part of the living body, is a constant concomitant of life. ”

“ An appeal made by Müller for observations on the development of the Caeciliae, and of those Amphibia which retain gills or gill-clefts throughout life, has unfortunately yielded no fruits.
In 1825 P. A. Latreille [6] published a new classification of the Vertebrata, which are primarily divided into Haematherma, containing the three classes of Mammifera, Monotremata and Aves; and Haemacryma, also containing three classes—Reptilia, Amphibia and Pisces. ”

“ But the increase of size which constitutes growth is the result of a process of molecular intussusception, and therefore differs altogether from the process of growth by accretion, which may be observed in crystals and is effected purely by the external addition of new matter—so that, in the well-known aphorism of Linnaeus, the word “grow” as applied to stones signifies a totally different process from what is called “growth” in plants and animals. ”

“ This, however, is not exactly accurate, if it be thereby implied that all living things have a visible organization, as there are numerous forms of living matter of which it cannot properly be said that they possess either a definite structure or permanently specialized organs: though, doubtless, the simplest particle of living matter must possess a highly complex molecular structure, which is far beyond the reach of vision. ”

“ Sir Richard Owen, in his work on The Anatomy of Vertebrates, followed Latreille in dividing the Vertebrata into Haematotherma and Haematocrya, and adopted Leuckart’s term of Dipnoa for the Amphibia. T. H. Huxley, in the ninth edition of this Encyclopaedia, treated of Brongniart’s Batrachia, under the designation Amphibia, but this use of the word has not been generally accepted. (See Batrachia.) (T. H. H.; P. C. M.)
↑ Brongniart’s Essai d'une classification naturelle des reptiles was not published in full till 1803. ”

“ In many low organisms, such as the spores of bacteria, the thick, non-conducting wall may preserve the living protoplasm from subjection to external temperatures below freezing point, or above boiling point, but all the evidence goes to show that applications of such cold or heat, if prolonged or arranged so as to penetrate to the living matter, destroy life. ”

“ Moreover, following the indications already given by K. E. von Baer in 1828, [5] Müller calls the attention of naturalists to the important fact, that while all the Squamata possess an amnion and an allantois, these structures are absent in the embryos of all the Nuda. ”

“ In warm-blooded animals, such as birds and mammals, protective mechanisms for the regulation of temperature enable them to endure exposure to extreme heat or cold, but in such cases the actually living cells do not appreciably rise or fall in temperature. A variation of a very few degrees in the blood itself produces death. ”

“ The properties of living matter are intimately related to temperature. Not only does exposure to heat sufficient to coagulate protein matter destroy life, by demolishing the molecular structure upon which life depends; but all vital activity, all phenomena of nutritive growth, Life conditioned by temperature.movement and reproduction are possible only between certain limits of temperature. ”

“ As has been said, a large proportion of water enters into the composition of all living matter; a certain amount of drying arrests vital activity, and the complete abstraction of this water is absolutely incompatible with either actual or potential life. But many of the simpler Life conditioned by moisture.forms of life may undergo desiccation to such an extent as to arrest their vital manifestations and convert them into the semblance of not-living matter, and yet remain potentially alive. ”

“ It may be safely said of all those living things which are large enough to enable us to trust the evidence of microscopes, that they are heterogeneous optically, and that their different parts, and especially the surface layer, as contrasted with the interior, differ physically and Life and organization.chemically; while, in most living things, mere heterogeneity is exchanged for a definite structure, whereby the body is distinguished into visibly different parts, which possess different powers or functions. Living things which present this visible structure are said to be organized ”

“ Thus an individual living body is not only constantly changing its substance, but its size and form are undergoing continual modifications, the end of which is the death and decay of that individual; the continuation of the kind being secured by the detachment of portions which tend to run through the same cycle of forms as the parent. ”

“ In the ordinary course of nature, all living matter proceeds from pre-existing living matter, a portion of the latter being detached and acquiring an independent existence. The new form takes on the characters of that from which it arose; exhibits the same power of propagating itself by means of an offshoot ”

“ There is reason to believe that carbonic acid is always one of these waste products, while the others contain the remainder of the carbon, the nitrogen, the hydrogen and the other elements which may enter into the composition of the protoplasm. ”

“ These limits may be set down as from a little above the freezing point of water to a little below the boiling point It is to be noted, however, that these limits apply to the living matter itself, and many of the apparent exceptions are due to cases in which the living matter is enclosed in protective wrappings capable of resisting heat and cold. ”

“ Physiology and its allied articles deal with the subject generally and in relation to man, while the special physiology of plants is dealt with in a section of the article Plants. Aetiology is treated of under the heading Evolution. ”