Bacteria / Especially as they are related to the economy of nature, to industrial processes, and to the public health

by Sir George Newman

A Method of Growing Cultivations in a Vacuum over Pyrogallic Solution

2. The Organisms of Nitrification. To this group belong the two chief types of nitrifying bacteria, viz., those which oxidise ammonia into nitrites, and those which change nitrites into nitrates.

3. The Nitrogen-fixing Bacteria, found mainly in the nodules on the rootlets of certain plants.

4. The Common Saprophytic Bacteria, whose function is at present but imperfectly known. Many are putrefactive germs.

5. The Pathogenic Bacteria. This division includes the three types, tetanus, malignant œdema, and quarter evil. Under this heading we shall also have to consider in some detail the intimate relation between the soil and such important bacterial diseases as tubercle and typhoid.

To enable us to appreciate the work which the "economic bacteria" perform, it will be necessary to consider shortly the place they occupy in the economy of nature. This may be perhaps most readily accomplished by studying the accompanying table (p. 145).

A SCHEME SHOWING THE PLACE AND FUNCTION OF THE ECONOMIC MICRO-ORGANISMS FOUND IN SOIL

Water		Chemical Substances [Nitrates, etc.]		Gases [CO2, H, N, O]
⬊		⬇		⬋
Plant Life
│
┌────────┬──────┬──────┬──────────┬───────────┐
Carbohydrates [albumoses, sugar, starch, etc.]	Fats	Proteids [bodies containing Nitrogen]	Vegetable Acids	Mineral Salts	Water
Animal Life
│
┌───────┬──────────┬──────────────────┐
Gases [CO2, etc.]	Water	Urea, Albuminoids, Ammonia compounds, etc.		Nitrogen in many forms locked up in the body
		PUTREFACTIVE AND DENITRIFYING BACTERIA │
	┌───────┬──────┬──────────┬───────────┐
	Free Nitrogen │ │ │ │ │ │ │ │	Gases [CO2]	Water	Ammonia and other elements of broken-down complex bodies.	[Nitrites]
				NITRIFYING BACTERIA
				│
				Nitrites[=Nitrous organism │ (Nitrosomans)]
	NITROGEN-FIXING BACTERIA			Nitrates[=Nitric organism (Nitrosomans)]
[In soil and in the nodules on the rootlets of Leguminosæ]				[In soil and available for plant life]

The threefold function of plant life is nutrition, assimilation, and reproduction: the food of plants, the digestive and storage power of plants, and the various means they adopt for multiplying and increasing their species. With the two latter we have little concern in this place. Respecting the nutrition of plant life, it is obvious that, like animals, they must feed and breathe to maintain life. Plant food is of three kinds, viz., water, chemical substances, and gas. Water is an actual necessity to the plant not only as a direct food and food-solvent, but as the vehicle of important inorganic materials. The hydrogen, too, of the organic compounds is obtained from the decomposition of the water which permeates every part of the plant, and is derived by it from the soil and from the aqueous vapour in the atmosphere. The chief chemical substances of which vegetable protoplasm is constituted are six, viz, potassium, magnesium, calcium, iron, phosphorous, and sulphur. These inorganic elements do not enter the plant as such, but combined with other substances or dissolved in water. Potassium occurs in salt form combined with various organic acids (tartaric, oxalic, etc.), calcium and magnesium as salts of lime and magnesia in combination both with organic and inorganic acids. Iron contributes largely to the formation of the green colouring matter of plants, and is also derived from the soil. Phosphorus, one of the chief constituents of seeds, generally occurs as phosphate of lime. Sulphur, which is an important constituent of albumen, is derived from the sulphates of the soil. In addition to the above, there are other elements, sometimes described as non-essential constituents of plants. Amongst these are silica (to give stiffness), sodium, chlorine, iodine, bromine, etc. All these elements contribute to the formation or quality of the protoplasm of plants.