Page:Insects - Their Ways and Means of Living.djvu/131

 ==CHAPTER IV: WAYS AND MEANS OF LIVING ==

IN our human society each individual must obtain the things necessary for existence; the manner by which he acquires them, whether by one trade or another, by this means or by that, does not physically matter so long as he provides himself and his family with food, clothing, and shelter. Exactly so it is wita all forms of lire. The physical demands of living matter make certain things necessary for the maintenance of lire in that matter, but nature has no law specifying that any necessity shall be acquired in a certain manner. Lire itself is a circumscribed thing, but it bas complete freedom of choice in the ways and means of living. It is useless to attempt to make a definition of what living matter is, or of how it differs from non-living matter, for all definitions have failed to distinguish animate from non-animate substance. But we all know that living things are distinguishable from ordinary non-living things by the fact that they make some kind of response to changes in the contact between themselves and their environment. The "environment," of course, must be broadly interpreted. Biologically, it includes all things and forces that m any way touch upon living matter. Not only bas every plant and animal as a whole its environment, but every part of it has an environment. The cells of an animal's stomach, for example, have their environment in the blood and lymph on one side, the contents of the stomach on the other; in the energy of the nerves distributed to them; and in the effects of heat and cold that penetrate them.