RELATION TO ENVIRONMENT— CLASSIFICATlOw 35 



Relation to Pressure. — High pressure does not exert any noticeable 

 effects upon bacteria. In the experiments of Certes/ a pressure of two 

 atmospheres seemed to have no influence upon the growth and motility 

 of anthrax bacilli suspended in blood. 



Relation to Moisture. — For the growth and development of all bac- 

 teria, the presence of water in the culture medium is necessary. It is 

 self-evident that nutritive materials can not be absorbed by an osmotic 

 process unless in a state of solution. While complete dryness does not 

 permit growth, its destructive action upon various bacteria is subject 

 to great differences. The effect of complete drying upon bacteria will 

 be found more fully discussed in the section upon the destruction of 

 bacteria by physical agents. (See page 62.) 



In the same section may be found a discussion of the effects of light, 

 electricity, x-ray, and radium rays upon bacteria. 



THE CLASSIFICATION OF BACTERIA 



Too simple in structure, too varied in biological properties to be 

 definitely identified with either the vegetable or animal kingdom, the 

 bacteria are placed at the bottom of the scale of all living beings. Closely 

 linked on the one hand to the plant kingdom by the yeasts and the 

 molds, and on the other to the animal kingdom by the protozoa, they 

 themselves combine, within one and the sa-me division, attributes so 

 widely divergent as to structure, metabohsm, and biological activity that 

 their grouping is more a matter of working convenience than of actual 

 scientific classification. Thus, for instance, all stages of metabolic ac- 

 tivity fill in the gap between the synthetizing sulphur and nitrifying 

 bacteria and the purely katabolic activities of some of the aerobic and 

 anaerobic microorganisms which cause putrefaction. Growth takes 

 place within the limits of a wide temperature range, and the specific 

 modes of life and cultural conditions are subject to the widest varia- 

 tions, from those of an indisputably useful saprophytism to those of the 

 most exquisite parasitism. Although, therefore, strictly speaking, the 

 bacteria can be classified as a whole neither in the animal nor in the 

 vegetable realms, being nonchlorophyll-bearing, they are for conve- 

 nience classified with the fungi or colorless plants. 



The relationship of the bacteria to other simple plants may be 

 graphically represented by the following scheme: 



I Certea, Compt. rend, de I'acad, d, sc, 99, Paris, 1884, 



