7. The fact that the egg, and probably every cell, has a definite structure should determine the limits of the divisibility of living matter. In most cases the complete destruction of a cell means the cessation of life phenomena. A brain or kidney which has been ground to a pulp is no longer able to perform its functions; yet we know that such pulps can still perform some of the characteristic chemical processes of the organ; _e. g._, the alcoholic fermentation characteristic of yeast can be caused by the press juice from yeast; or characteristic oxidations can be induced by the ground pulp of organs. The question arises as to how far the divisibility of living matter can be carried without interfering with the total of its functions. Are the smallest particles of living matter which still exhibit all its functions of the order of magnitude of molecules and atoms, or are they of a different order? The first step toward obtaining an answer to this question was taken by Moritz Nussbaum,[139] who found that if an infusorian be divided into two pieces, one with and one without a nucleus, only the piece with a nucleus will continue to live and perform all the functions of self-preservation and development which are characteristic of living organisms. This shows that at least two different structural elements, nucleus and cytoplasm, are needed for life. We can understand to a certain extent from this why an organ after being reduced to a pulp, in which the differentiation into nucleus and protoplasm is definitely and permanently lost, is unable to accomplish all its functions.[140] [139] Nussbaum, M., _Arch. f. mikroscop. Anat._, 1886, xxvi., 485. [140] It must not be overlooked that in bacteria and the blue algæ no distinct differentiation into nucleus and protoplasm can be shown. To these organisms, therefore, the experiments of Nussbaum cannot be applied.