52 Biological Conditions 



expedition ; it is, however, certain that these minute organisms were 

 introduced on to the island and began to develope as soon as, possibly 

 even before, the algae and spores. 



Dr E. De Kruyff, Bacteriologist to the Agricultural Department of 

 Buitenzorg, was kind enough to provide me with sterilised tubes and 

 appliances for obtaining samples of earth, also a culture-plate for 

 the enumeration of Mould-Fungi ; he generously undertook the 

 examination of our material. The bacteriological investigations based 

 on four samples of soil (two samples from the Barringtonia and 

 Casuarina forests, one sample from the strand-zone, one sample from 

 the interior of the island) demonstrated the occurrence of between 

 1,300,000 and 2,800,000 (the average of four samples 2,200,000) 

 bacteria in 1 gramme of soil, figures which agree with those ob- 

 tained by De Kruyff from an examination of the soil at Buitenzorg 

 in Java and with the results of similar calculations in regard to 

 various soils in Switzerland. 



The number of the bacteria species identified is not large, but it 

 is important to notice that they belong to very different biological 

 groups. Among the ordinary soil-bacteria, Bacillus mycoides and 

 Bacillus Moire' (B. Megatherium De Bary ?) were abundant, and 

 Bacillus fluoresceins liquaefaciens among typical putrefactive 

 bacteria. 



All four samples afforded examples of bacteria which destroy 

 cellulose, pectin, and starch, as well as Urobacteria, the bacteria 

 which decompose urea, a fact of some interest in view of the feeble 

 development of animal-life on the island. Several Moulds were found 

 on the culture-plate, but it is remarkable that no Yeasts occurred 

 either on the plates or in the samples of earth. By far the most 

 important fact from the point of view of the nutrition of vascular 

 plants on Krakatau is the occurrence of such bacteria as play an 

 important part in the circulation of nitrogen, the nitrite- and nitrate- 

 bacteria and the nitrogen-fixing bacteria. 



As the result of the disintegration of the nitrogenous substances 

 of dead animals and plants by putrefactive bacteria and other micro- 

 organisms the nitrogenous compounds are largely converted into 

 ammonia. A portion of the ammonia which is thus produced is fixed 

 by the soil and afterwards converted by the action of nitrite- and 

 nitrate-bacteria into nitrous and nitric acids which are readily taken 

 up in the form of salts by the absorbing organs of vascular plants. 

 Another portion of the ammonia is given off into the air as gas and 

 some of it is given back to the soil by the rain in combination with 

 nitric, nitrous and carbonic acids. 



In the interior of the island also a considerable quantity of 



