TECHNIC BACTERIOLOGICAL EXAMINATION OF SOILS. 

 Table VI — Continued. 



297 



This table shows : 



That the errors in measuring which might occur in using pipettes are 

 magnified when made in taking a 1 cc aliquot. 



Table VI in Comparison to Table V. 



(1) Errors of .01 to .02 of a cc that may occur in using a 1 cc pipette 

 cause a larger error in the high bacterial dilutions than the volume of ordinary 

 soil contained in the aliquot does. 



(2) That the slightly larger error caused by the volume of ordinary soil 

 in 10 cc aliquots of soil and water mixtures is more than offset by the accuracy 

 with which the ten cc aliquots can be measured. 



Adding Water to Dilution Bottles. 



The water is not sterihzed in the dilution bottles, because: 

 Water is lost from the dilution bottles if it is sterilized in them, and 

 The amount lost varies with: 



1. The autoclave. 



2. The size of the load in the autoclave. 



3. The variation in hardness of the cotton plugs in the bottles. 



4. The position of the bottle in the autoclave. 



5. The siu^aee of liquid exposed and the amount of liquid in the bottle. 



The following tests show the results of one sterilization in the autoclave. 

 In putting the water into the eight ounce bottles used in these tests the teehnic 

 was as follows : Each bottle was weighed to the nearest decigram and 99 gms., 

 or 90 gms., as desired, in excess of the weight of the bottle was placed on the 



