Before anything can be said of the conclusions in this branch of science one preliminary remark has to be made. From the philosophical point of view the science of life includes all other, for man is a living animal, and science is the work of his co-operating mind, one of the functions of his living activity. What this involves on the philosophical side does not concern us here, but it is necessary to indicate here the nature of the contact between the two great divisions of science, the mechanical and the biological, considered purely as sciences. For, though we know that our consciousness as a function of life must in some form come into the science of life, and is, in a sense, above it all, we are yet able to draw conclusions, apparently of infinite scope, about the behaviour of all living things around us and including ourselves, just as we do about a stone or a star. And we are interested in this chapter in seeing how this drawing of general conclusions keeps growing with regard to the phenomena of life, just as it has grown with regard to all other phenomena, and we have to consider what sort of difference there is between the one class of generalizations and the other. For those of us who are content to rest their conclusions on the positively known, who, while not setting any limits to the possible extension of knowledge, are not prepared to dogmatize about it, it is still necessary to draw a line. A dualism remains, name and fact alike abhorrent to the completely logical philosophic mind. On the one hand the ordinary laws of physical science are constantly extending their sphere; on the other, the fact of life still remains unexplained by them, and becomes in itself more and more marvellous as we investigate it. The general position remains much as Johannes Mueller expressed it about the middle of the last century, himself sometimes described as the central figure in the history of modern physiology. 'Though there appears to be something in the phenomena of living beings which cannot be explained by ordinary mechanical, physical, or chemical laws, much may be so explained, and we may without fear push these explanations as far as we can, so long as we keep to the solid ground of observation and experiment.' Since this was written the double process has gone on apace. The chemistry and physics of living matter are being sketched, and biologists are more and more inclined to study the mechanical expression of the facts of life. Mr. Bateson, for instance, tells us that the greatest advance that we can foresee will be made 'when it is possible to connect the geometrical phenomena of development with the chemical'. The process of applying physical laws to life follows, it would seem, the reverse order of their original development. First the chemistry of organic matter was investigated, then the physical attraction of their molecules, and now their geometry is in question.