compounds, from the elements of which the body cells may construct their own material, or else renew their supply of energy. In the latter case, too, as has been mentioned before, a preparatory decom- position (a kind of adaptation to the cell) is necessary.
An analogy may be used to make clear this kind of reconstruction. Suppose an architect is called upon to convert a certain building, which has been specially designed for a particular purpose, into one suitable for an entirely different object. He would only be able to carry out this work on the condition that he might pull down the original structure. He would naturally be able to work some of the bricks of the old building into the plans of his new one. Some of the bricks, or even combinations of bricks, may be used as they are, others will have to be recut, while others, again, are of no value whatever. In just the same way does the animal organism act towards the specifically constructed parts of the cells which are used as food. First of all comes the disintegration into simple compounds, and then a reconstruction, according to entirely new plans, on the other side of the intestines.
The simplest conditions, in this respect, are to be seen amongst mammals during the suckling period, when, under normal conditions, the animal imbibes the milk peculiar to its species. This, as G. von Bunge first demonstrated very precisely, is in every
