The evolution of living organisms / by Edwin S. Goodrich.

  • Edwin Stephen Goodrich
Date:
[1912]
Catalogue details

Licence: Public Domain Mark

Credit: The evolution of living organisms / by Edwin S. Goodrich. Source: Wellcome Collection.

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    their supply of carbon. Among the multitude of bacteria which abound in the soil there are many which can build up proteins, and therefore protoplasm, from inorganic compounds alone ; and some indeed which can make use of the free nitrogen of the air. All the phenomena of life are associated with the physico-chemical processes of metabolism taking place in protoplasm alone. The three most characteristic properties of living matter : irritability, or the power to respond to stimuli, growth, and reproduction, all depend on metabolism. An excess of anabolic over katabolic processes leads to increase of protoplasm, to growth, and ultimately to reproduction. An excess of katabolic over anabolic processes leads, on the contrary, to reduction and to death. Like all physico-chemical processes, metabolism is limited by definite conditions. The essential elements must be present, and a sufficiency of food to balance the waste. Water is another essential, since all the chemical reactions really take place in solutions. Free oxygen is also necessary for the burning of the food material, ex¬ cept in the rare case of certain parasitic organisms and bacteria, which can obtain it from compound substances. Moreover, metabolism can only take place at all within a somewhat narrow range of temperature, the exact limits of which vary with different organisms. No metabolism is, of course, possible at a temperature so high as to coagulate or destroy the pro terns, or so low as to stop chemical action. Most, perhaps all, of the processes of metabolism take place with the help of special proteins, known as ferments or enzymes, which have the property of facilitating and hastening chemical actions. Just as a small trace of platinum black will cause an indefinitely large amount of hydrogen peroxide (H202) to decompose into oxygen and water, so a small quantity of ferment will cause an inde¬ finitely large amount of carbohydrate, fat, or protein, to break up into simpler substances. Such ferments, which are not themselves affected, which are not involved in the end products of the actions they facilitate, are called