[Illustration: Fig. 8. _Peranema._ A--Swimming in non-stimulated condition. B--Mechanically stimulated at the end of the flagellum.] Another instance. A number of fertilized eggs of the sea urchin are placed in a watch glass in sea water. The temperature of the water should correspond with the mean temperature in which the animals live in the sea, averaging about 15° C. The eggs begin to form grooves and to develop slowly by progressive division. In another glass we observe a second sample of fertilized eggs of the same kind and under the same conditions, but in this case we increase the temperature to 25° C. The increased temperature brings about a decided increase of segmentation and the same stage of development is reached in less than half the time. The increased temperature, therefore, increases the development. Further we take a third sample of the same urchin eggs in a watch glass with sea water of 15° C. and add a little sea water mixed with ether. The development of the eggs now comes to a standstill. The narcotic has produced an inhibition of development. To quote another instance. _Bacterium phosphorescens_ having been bred upon a putrid fish are exposed in the culture fluid to the air. In the dark the bacteria give forth a phosphorescent light. Then the culture fluid containing the bacteria is put into a glass receptacle, which can be rendered air-tight and all oxygen excluded. After a short time the light formation ceases completely. The absence of oxygen has here had a depressing effect and it is only after air has been again introduced that light is once more produced. Lastly, an example from the group of mammals may be cited. The metabolism of a dog in complete rest is examined for a prolonged length of time and we ascertain the values of the oxygen consumption, the carbon dioxide production, and the nitrogen elimination in the urine. Under the same nutritive conditions the animal is then allowed to work from time to time in a treadmill. During these working periods impulses of excitation are continually conducted to the muscles from the nervous system. It is now found that under the influence of the constantly recurring stimuli the quantity of nitrogen in the urine has only very slightly augmented, whereas the consumption of oxygen and the production of carbon dioxide has markedly increased.