CHAPTER III 



LIVING MATTER: CONDITIONS BY WHICH IT IS DETERMINED 



CONTENTS. 1. Nutrition the necessary external condition of vital metabolism. 

 Phenomena of inanition. 2. Importance of water. Latent life and anabiosis. 

 3. Importance of oxygen. Aerobic and anaerobic life. 4. External temperature 

 indispensable to life. 5. Total pressure of air and water, and partial pressure of 

 oxygen and carbonic acid. 6. External stimuli. 7. Chemical stimuli. Chemo- 

 taxis. 8. Mechanical stimuli. Barotaxis. 9. Thermal stimuli : thermotaxis. 

 10. Photic stimuli. Phototaxis and Heliotaxis. 11. Electrical stimuli. Galvano- 

 taxis. 12. The various biological zones of ocean life (Plankton). 13. Internal 

 conditions and stimuli of metabolism. Theory of automatism. 14. Hypotheses 

 to explain the intimate mechanism of living matter. Bibliography. 



Two orders of conditions, external and internal, are essential to 

 the maintenance of metabolism. Both the one and the other may 

 act directly or indirectly. The former cannot fail without cessation 

 of life, nor the latter without modifications and disturbances of 

 vital phenomena. If we were acquainted with all the internal and 

 external conditions of life, the task of Physiology would be 

 terminated ; the " conditioned," i.e. Life, would be perfectly known 

 to us. 



Not all the vital conditions are essential in the same degree to- 

 every living being. Each organism has special requirements in 

 virtue of which it lives and nourishes. Each living species, there- 

 fore, demands special treatment. From the standpoint of general 

 physiology we have only to consider in broad outlines the most 

 universal and best known of the vital conditions. 



I. The first and most general external condition of metabolism 

 is Nutrition, i.e. the sum of the chemical materials essential to the 

 building-up of living protoplasm. 



We saw in the last chapter how various were the chemical 

 forms of the foods necessary to different groups of living beings 

 to nitrifying bacteria, green plants, saprophytic and parasitic fungi, 

 herbivorous and carnivorous animals. To this we may add that 

 in accordance with the chemical composition of the nutritive 

 medium, the various elementary organisms react very differently. 

 Some can only live in fresh water ; others in salt water. All die 

 more or less rapidly when brought into distilled water. Every 



