34 



under glass gave no less than 5 additional tons of fruit per acre, 

 worth between £250 and £300. 



Some of the substances are solids and are easily handled 

 and applied. The significance of the advances made in recent 

 years in these laboratories will be appreciated when it is recalled 

 that the first agents used were highly inflammable substances, 

 difficult and expensive to transport, and that they were applied 

 to the soil at the rate of 10 tons per acre by means of a special 

 injector — another difficult and costly process. These dangerous 

 liquids were soon replaced by a crude cresylic acid (called carbolic 

 acid), an oily liquid watered into the ground at the rate of 2f 

 tons per acre — but the process was still expensive, the material 

 alone costing over £160, while the labour was considerable. 

 The new substances are solids, and are so potent that 2 cwt. per 

 acre has proved effective. Although they are not as yet on the 

 market, there seems no reason why they should not be made as 

 intermediate products in connection with one of the large 

 organic chemical industries, such as the making of dyes. It 

 is essential to success that the added substances should be 

 removed from the soil as soon as their work is done, otherwise 

 they may injure the plant : this removal is accomplished by a 

 perfectly natural process. Although the compounds are so 

 poisonous to certain undesirable organisms, they serve as food 

 and energy materials to others among the remarkable population 

 of the soil — an illustration from the lowliest type of life of the 

 old adage : " What is one man's meat is another man's poison." 



Among the phenol destroying bacteria one has been found 

 by Mr. Gray to possess the interesting property of converting 

 indol into indigo — a change of great biochemical interest. 



The laboratory studies of the effects of partial sterilisation 

 on the soil microorganisms have been continued by Mr. Cutler 

 and Miss Dixon, using heat and phenol as the two agents ; applica- 

 tion of either results in an increase in the numbers of bacteria and 

 the destruction of active protozoa, but the course of events is not 

 the same in the two cases. Phenol induces rapid multiplication of 

 specialised types of bacteria capable of using it as a source of 

 energy, but the general bacterial population undergoes little 

 change. Moreover, when applied in small quantities, the phenol 

 does not kill the protozoan cysts ; these remain dormant until it 

 has disappeared, and then resume their active existence. A 

 temperature of 65° C. causes the complete destruction of protozoa 

 and an initial depression of the bacteria. Subsequently the 

 bacteria increase and attain high numbers which are kept up for 

 long periods. 



It has been found that this partial sterilisation effect takes 

 place within relatively short ranges of temperature; 55° C. or 

 less does not bring it about, but 65° C. gives a result as marked 

 as that of higher temperatures. It is worthy of note that 

 65° C. is the death point for soil protozoa. 



An interesting problem has arisen as to the effect of storage 

 of the soil in bottles or open jars on the soil population. When 

 SOU is taken from the field, and after sieving placed in bottles, 





