“He was one of those simple, disinterested, and intellectually sterling workers to whom their own personality is as nothing in the presence of the vast subjects that engage the thoughts of their lives.” John Morley. (Article Diderot, Encyclopædia Britannica .)...

It is generally admitted that the individual physio­logical processes, such as diges­tion, metabolism, the produc­tion of heat or of electricity, are of a purely physico­chemical character; and it is also conceded that the func­tions of individual organs, such as the eye or the ear, are to be analysed from the viewpoint of the physicist. When, however, the biologist is confronted with the fact that in the organism the parts are so adapted to each other as to give rise to a harmonious whole; and

1. The physical researches of the last ten years have put the atomistic theory of matter and electricity on a definite and in all probability permanent basis. We know the exact number of molecules in a given mass of any substance whose molecular weight is known to us, and we know the exact charge of a single electron. This permits us to state as the ultimate aim of the physical sciences the visualiza­tion of all phenomena in terms of groupings and displacements of ultimate particles, and since t

1. Each organism is characterized by a definite form and we shall see in the next chapter that this form is determined by definite chemical substances. The same is true for crystals, where substance and form are definitely connected and there are further analogies between organisms and crystals. Crystals can grow in a proper solu­tion, and can regenerate their form in such a solu­tion when broken or injured; it is even possible to prevent or retard the forma­tion of crystals in a supersaturated

1. It is a truism that from an egg of a species an organism of this species only and of no other will arise. It is also a truism that the so-called protoplasm of an egg does not differ much from that of eggs of other species when looked at through a microscope. The ques­tion arises: What determines the species of the future organism? Is it a structure or a specific chemical or groups of chemicals? In a later chapter we shall show that the egg has a simple though definite structure, but in this c

1. We have become acquainted with two characteristics of living matter: the specificity due to the specific proteins characteristic for each genus and possibly species and the synthesis of living matter from the split products of their main constituents instead of from a supersaturated solu­tion of their own substance, as is the case in crystals. We are about to discuss in this and the next chapter a third characteristic, namely, the phenomenon of fertiliza­tion. While this is not found in all o

1. The majority of eggs cannot develop unless they are fertilized, that is to say, unless a spermato­zoön enters into the egg. The ques­tion arises: How does the spermato­zoön cause the egg to develop into a new organism? The spermato­zoön is a living organism with a complicated structure and it is impossible to explain the causa­tion of the development of the egg from the structure of the spermato­zoön. No progress was possible in this field until ways were found to replace the action of the li

1. The writer in a former book ( Dynamics of Living Matter , 1906, p. 1), defined living organisms as chemical machines consisting chiefly of colloidal material and possessing the peculiarity of preserving and reproducing themselves. Some authors like Driesch, and v. Uexküll seem to find it impossible to account for the development of such machines from an undifferentiated egg on a purely physico­chemical basis. A study of Driesch’s very interesting and important book 116 shows that he assumes t

1. The action of the organism as a whole seems nowhere more pronounced than in the phenomena of regenera­tion, for it is the organism as a whole which represses the phenomena of regenera­tion in its parts, and it is the isola­tion of the part from the influence of the whole which sets in action the process of regenera­tion. The leaf of the Bermuda “life plant”— Bryophyllum calycinum —behaves like any other leaf as long as it is part of a healthy whole plant, while when isolated it gives rise to

1. It is a general fact that both sexes appear in approximately equal numbers, provided a sufficiently large number of cases are examined. This fact has furnished the clue for the discovery of the mechanism which determines the relative number of the two sexes. The honour of having pointed the way to the solu­tion of the problem belongs to McClung. 182 It has been known that certain insects, e. g. , Hemiptera and Orthoptera, possess two kinds of spermatozoa but only one kind of eggs. The two kin

1. The scientific era of the investiga­tion of heredity begins with Mendel’s paper on plant hybridiza­tion which was not appreciated by his contemporaries. Mendel invented a method for the quantitative study of heredity which consisted essentially in crossing two forms of peas differing only in one well-defined hereditary character; and in following statistically and separately the results of this crossing and that of the inbreeding of the second and third genera­tions of hybrids. This led him t

1. The idea that the organism as a whole cannot be explained from a physico­chemical viewpoint rests most strongly on the existence of animal instincts and will. Many of the instinctive actions are “purposeful,” i. e. , assisting to preserve the individual and the race. This again suggests “design” and a designing “force,” which we do not find in the realm of physics. We must remember, however, that there was a time when the same “purposefulness” was believed to exist in the cosmos where everyth

1. The term environ­ment in rela­tion to an organism may easily assume a mystic rôle if we assume that it can modify the organisms so that they become adapted to its peculiarities. Such ideas are difficult to comprehend from a physico­chemical viewpoint, according to which environ­ment cannot affect the living organism and non-living matter in essentially different ways. Of course we know that proteins will as a rule coagulate at temperatures far below the boiling point of water and that no life

1. It is assumed by certain biologists that the environ­ment influences the organism in such a way as to increase its adapta­tion. Were this correct it would not contradict a purely physico­chemical concep­tion of life; it would only call for an explana­tion of the mechanism by which the adapta­tion is brought about. There are striking cases on record which warn us against the universal correctness of the view that the environ­ment causes an adaptive modifica­tion of the organism. Thus the write

Darwin’s work has been compared to that of Copernicus and Galileo inasmuch as all these men freed the mind from the incubus of Aristotelian philosophy which, with the efficient co-opera­tion of the church and the predatory system of economics, caused the stagna­tion, squalor, immorality, and misery of the Middle Ages. Copernicus and Galileo were the first to deliver the intellect from the idea of a universe created for the purpose of man; and Darwin rendered a similar service by his insistence t

1. It is an old saying that we cannot understand life unless we understand death. The dead body, if its temperature is not too low and if it contains enough water, undergoes rapid disintegra­tion. It was natural to argue that life is that which resists this tendency to disintegra­tion. The older observers thought that the forces of nature determined the decay, while the vital force resisted it. This idea found its tersest expression in the defini­tion of Bichat, that “life is the sum total of th