Jacques Loeb

“ It is this positive helio­tropism which makes them move upward where they find their food, when the mild air of the spring calls them forth from their nest. At the top of the branch, they come in contact with a leaf, and chemical or tactile influences set the mandibles of the young caterpillar into activity. If we put these larvæ into closed test-tubes which lie with their longitudinal axes at right angles to the window, they will all migrate to the window end, where they stay and starve, even if their favourite leaves are close behind them. They are slaves of the light. ”

“ The work on Mendelian heredity has shown that an extremely large number of independently transmissible Mendelian factors help to shape the individual. It is not yet proven that the organism is nothing but a mosaic of Mendelian factors, but no writer can be blamed for considering such a possibility. If we assume that the organism is nothing but a mosaic of Mendelian characters it is difficult indeed to understand how they can force each other into a harmonious whole6; even if we make ample allowance for the law of chance and the corresponding wastefulness in the world of the living. ”

“ We must remember that all the cells of an organism have identical chromo­somes, so that a factor for an enzyme like tyrosinase is contained in every cell throughout the whole body. It is likely, however, that the same factor (which we may conceive to be a definite chemical compound) will find a different chemical substrate to work on in the cells of different organs of the body, since the different organs differ in their chemical composi­tion. ”

“ We can only know the material conditions and not the intimate nature of life phenomena. We have therefore only to deal with matter and not with the first causes or the vital force derived therefrom. These causes are inaccessible to us, and if we believe anything else we commit an error and become the dupes of metaphors and take figurative language as real. ”

“ It is true that a crystal can grow, but it will do so only in a supersaturated solu­tion of its own substance. Just the reverse is true for living organisms. In order to make bacteria or the cells of our body grow, solu­tions of the split products of the substances composing them and not the substances themselves must be available to the cells; second, these solu­tions must not be supersaturated, on the contrary, they must be dilute; and third, growth leads in living organisms to cell division as soon as the mass of the cell reaches a certain limit. ”

“ The constant synthesis then of specific material from simple compounds of a non-specific character is the chief feature by which living matter differs from non-living matter. With this character is correlated another one; namely, when the mass of a cell reaches a certain limit the cell divides. This is perhaps most obvious in bacteria which on the proper nutritive medium take up food, grow, and divide into two bacteria, each of which takes up food, divides, and grows ad infinitum, as long as the food lasts, provided the harmful products of metabolism are removed. ”

“ The reason that an egg once fertilized with sperm cannot be fertilized again may be found in a group of facts which we will now discuss, namely, the self-sterility of many hermaph­ro­dites. The fact that hermaph­ro­dites are often self-sterile, while their eggs can be fertilized with sperm from a different individual of the same species has played a great rôle in the theories of evolu­tion. We are here only concerned with the mechanism which determines the block to the entrance of a spermato­zoön into an egg of the same hermaph­ro­ditic individual. ”

“ This idea found its tersest expression in the defini­tion of Bichat, that “life is the sum total of the forces which resist death.” Science is not the field of defini­tions, but of predic­tion and control. The problem is: first, how does it happen that as soon as respira­tion has ceased only for a few minutes the human body is dead, that is to say, will commence to undergo disintegra­tion, and second, what protects the body against this decay while the respira­tion goes on, although temperature and moisture are such as to favour decay? ”

“ However, the analogies between a living organism and a crystal are merely superficial and it is by pointing out the fundamental differences between the behaviour of crystals and that of living organisms that we can best understand the specific difference between non-living and living matter. ”

“ These facts agree with the suggestion of Fermi that in the living cell the proteins cannot be attacked by the digestive enzymes but relieves us of the necessity of making the monstrous assump­tion of a “living molecule” of proteins as distinct from a “dead” molecule. The difference between life and death is not one between living and dead molecules, but more likely between the excess of synthetic over hydrolytic processes. ”

“ It is quite possible that the apparent immunity to a transplanta­tion of cancer produced by Jensen, Leo Loeb, and Ehrlich and Apolant through the previous transplanta­tion of tissue in such an animal was due to the fact that this previous tissue transplanta­tion led to an increase in the number of lymphocytes in the animal. The medical side, however, lies outside of our discussion, and we must satisfy ourselves with only a passing notice. The facts show that each warm-blooded animal seems to possess a specificity whereby its lymphocytes destroy transplanted tissue taken from a foreign species. ”

“ The light, which saved its life by making it creep upward where it finds food, would cause it to starve could it not free itself from the bondage of positive helio­tropism. The animal, after having eaten, is no longer a slave of the light, but can and does creep downward. ”

“ By inheritance the mass of enzymes is approximately the same and in this way all the embryos beat at the same rate (within the limits of the fluctuating varia­tion) at the same temperature. This identity exists, however, only as long as the embryo is relatively quiet in the egg. As soon as the embryo begins to move this equality disappears since the motion influences the heart-beat and the motility of different embryos differs.
In man the number of disturbing factors is so great that no equality of the rate for the same temperature can be expected. ”

“ And yet we are better off in regard to our knowledge of the instincts than we are in regard to morphogenesis, as in the former we can show that the apparent instincts in some cases obey simple physico­chemical laws with almost mathematical accuracy. Since the validity of the law of gravita­tion has been proved for the solar system the idea of design in the motion of the planets has lost its usefulness, and this fact must serve us as a guide wherever we attempt to put science beyond the possibility of mysticism. ”

“ If Arrhenius is right that living matter has had no more beginning than matter in general, this hope of making living matter artificially appears at present as futile as the hope of making molecules out of electrons. ”

“ In other words, the adapta­tion of blind animals to the cave is only apparent; they were adapted to cave life before they entered the cave. Many animals are obviously burdened with a germinal abnormality giving rise to imperfec­tion and smallness of the eye—the hereditary factor involved may have to do with the development of the blood-vessels and lymphatics of the eye. Such mutants can survive more easily in the cave, where they do not have to meet the competi­tion of seeing forms, than in the open. In man also an hereditary form of blindness is known, the so-called hereditary glaucoma. ”

“ Should the caterpillars move down the shrub, they would starve, but this they never do, always crawling upward to where they find their food. What gives the caterpillar this never-failing certainty which saves its life, and for which a human being might envy the little larva? ”

“ 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. ”

“ It is purely due to limita­tion of food that bacteria or certain species of them do not cover the whole planet. But, as every layman knows, the majority of organisms grow only to a certain size, then die, and the propaga­tion takes place through sex cells or gametes: a female cell—the egg—containing a large bulk of protoplasm (the future embryo) and reserve material; and the male cell which in the case of the spermato­zoön contains only nuclear material and no cytoplasmic material except that contained in the tail which in some and possibly many species does not enter the egg. ”

“ 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 new plants. ”

“ As soon as we can show that a life phenomenon obeys a simple physical law there is no longer any need for assuming the action of non-physical agencies. We shall see that this has been accomplished for one group of animal instincts; namely those which determine the rela­tion of animals to light, since these are being gradually reduced to the law of Bunsen and Roscoe. This law states that the chemical effect of light equals the product of intensity into dura­tion of illumina­tion. Some authors object to the tendency toward reducing everything in biology to mathematical laws or figures ”