September 19, 1913] 



SCIENCE 



415 



medium, i. e., _ the peptone solution, is used as 

 basis, ammonification is most rapid in the driest 

 soil (10 per cent, water). If the data are com- 

 puted per 100 c.e. of soil solution, the concentra- 

 tion of the solution is again of greatest impor- 

 tance. The results vary greatly if one time the 

 peptone is given in proportion to the amount of 

 soil and another time in proportion to the amount 

 of soil moisture. The farmer is primarily inter- 

 ested in the amount of plant food per weight of 

 soil; the efficiency of bacteria can be determined 

 only by comparing equal amounts of culture me- 

 dium and of food. In test tube or flask cultures 

 of B. mycoides, oxygen is always in the minimum. 

 In sand cultures, the oxygen exchange is greatly 

 increased and the rate of development is corre- 

 spondingly higher. The oxygen exchange between 

 gas and liquid depends upon the oxygen content 

 of the soil air and upon the surface exposed to 

 this air. The surface per unit of liquid is in- 

 versely proportional to the diameter of the soil 

 particles and to the moisture content of the soil. 

 The oxygen content of the soil air depends upon 

 the ventilation which is nearly proportional to the 

 square of the grain diameter. A thinner film of 

 moisture gives therefore a faster decomposition, 

 but there is a limit to the thinness of this film, 

 extremely thin films causing a retarded decomposi- 

 tion. The optimum thickness of moisture film in 

 the ease of B. inycoides was between 20 and 40 

 microns. This film was obtained in sand of 1 mm. 

 diameter at a moisture content of about 10 per 

 cent. In arable soils, with a grain size not more 

 than 0.1 mm., it would require more than 50 per 

 cent., of moisture to produce the optimum film 

 thickness. In other words, strictly aerobic bac- 

 teria will never find optimum conditions of exist- 

 ence in soils. The ultimate endpoint of decom- 

 position, if the food concentration was constant, 

 was the same in the case of B. mycoides, since only 

 the rate of decomposition was influenced by the 

 efficiency of the oxygen supply. With some other 

 bacteria, the endpoint varied greatly. The be- 

 havior of anaerobic bacteria, represented by Bad. 

 lactis acidi, was in accordance with the above- 

 mentioned principles, the main factor for their 

 development being a very thick moisture film. 

 The physical effects of undecomposed organic mat- 

 ter were imitated by the addition of finely ground 

 filter paper to sand. In fairly dry soils, cellulose 

 caused a decrease of ammonia formation by 

 making some of the soil moisture unavailable for 

 bacteria. In the moisture sands, cellulose in- 



creased the ammonification probably by holding 

 the sand particles farther apart and thus in- 

 creasing aeration. 



Cliaract eristics of Cellulose-destroying Bacteria: 

 I. G. McBeth, F. M. Scales and N. E. Smith. 

 Seventeen species of cellulose-destroying bac- 

 teria have been isolated and studied; 7 of these 

 belong to the genus Bacillus, 4 to the genus Bac- 

 terium and 6 to the genus Pseudomonas. All are 

 morphologically and physiologically different from 

 Omelianski's hydrogen and methane ferments. 

 None of the species studied have shown any tend- 

 ency to form gaseous products, and in relation to 

 oxygen all are facultative aerobes. By means of 

 cellulose agar colonies the species may be sepa- 

 rated into two distinct groups: those forming 

 opaque colonies which clear a well-defined zone 

 beyond the colony and those which form trans- 

 parent colonies with little or no indication of an 

 enzymio zone. All of the organisms grow more or 

 less rapidly on beef gelatin, but only 10 of the 

 17 species studied have shown any power to liquefy 

 gelatin. On beef agar 11 species grow rapidly and 

 luxuriantly, 4 species grow poorly and 2 have 

 failed to give any growth at all. When introduced 

 into Dunham's solution 9 species have shown the 

 power to form ammonia. The action on litmus 

 milk is also quite variable; 10 species give an 

 acid reaction, 5 an alkaline reaction and 2 make 

 no growth. The digestion of the milk occurred 

 with only 4 species. Eleven species have shown a 

 growth on potato cylinders while 6 have shown no 

 growth or only a slight bleaching action along the 

 track of the inoculum. The action of the cellulose- 

 destroying bacteria studied shows marked differ- 

 ences in their activity toward the other carbohy- 

 drates such as dextrose, lactose, maltose, sac- 

 charose, glycerine, mannite and starch in peptone 

 solutions. In their relation to these solutions the 

 cellulose-destroying organisms may be divided into 

 the following groups: (1) those which give an 

 acid reaction from all of seven peptone carbohy- 

 drate solutions used; (2) those which give an 

 alkaline reaction from all of the peptone carbo- 

 hydrate solutions; (3) those which give an acid 

 reaction from only a part of the peptone carbo- 

 hydrate solutions; (4) those which produce no 

 change in the reaction of any of the peptone 

 carbohydrate solutions. 



A Flan for Revivifying Bacteria by Groups: H., 

 J. Conn. 



Our present standard method of revivification, 

 in non-saccharine broth at 37°, is not applicable 



