222 LECTURE XL 



The fully developed organism has, of course, losses. We need only 

 refer to its secretions, to the constant changes of the epidermal struc- 

 tures, the cells of the mucous membrane, and to all of the observa- 

 tions regarding the organs themselves, which participate in a continuous 

 decomposition and reconstruction in the tissues. It is, of course, possible 

 that these latter processes are much more extensive than we have any 

 idea, and that new groups are constantly entering the cell contents, 

 and others leaving. This is in accord with the fact that the animal 

 organism disintegrates the nutrients to such an extent and adapts them 

 to all of the bodily requirements. On the other hand, we can form 

 no clear conception of the manner in which protoplasm and its com- 

 ponents are used up, nor understand at present why the cells should tear 

 down its own components in order to make way for the constituents of 

 the nourishment. As the different cells, according to the tissues of which 

 they are a part, and the function which they serve, have a specific 

 structure, and above all possess individualized protein materials, we must 

 consequently assume that the cells at every moment take their own char- 

 acteristic building material from the homogeneous mixture of the blood 

 proteins, and to some extent transform them in a quite complicated 

 manner. It is possible that the whole phenomenon is an hereditary one. 

 The single-celled organisms are constantly engaged in multiplying them- 

 selves. They develop rapidly, producing new individuals in quick suc- 

 cession. We meet the same phenomenon in some of the more highly 

 organized invertebrates. From a single individual, thousands and tens of 

 thousands of new, rapidly growing creatures are formed. The whole cell 

 material is engaged in constant growth and change. We also find analo- 

 gous phenomena among the vertebrates. In these cases they are confined 

 in the grown individual to the sexual organs. Here, also, we observe a 

 constant increase in the number of cells, and a continual delivery of cell 

 material, on the one hand eggs, and on the other spermatozoa. The 

 cooperative efficiency of the other body-cells, in promptly preparing thou- 

 sands and tens of thousands of new cells, is evident from the tremendous 

 production of leucocytes at the beginning of any infection. The invading 

 army is surrounded in the shortest space of time by thousands of white 

 blood-corpuscles. They form a thick wall, and protect the remainder of 

 the organism. The leucocytes also play some other, as yet undiscovered, 

 important role in the animal organism. For instance, they are present in 

 the intestines in large numbers during digestion. Every one of these 

 newly formed cells must have a completely-constructed protoplasm. They 

 must in every case contain all the elementary components; moreover, they 

 also contain proteins, which alone are capable of giving to their compli- 

 cated structure its true individuality. 



The great facility with which the animal organism produces new cells 



