352 TEXT-BOOK OP BACTERIOLOGY. 



particles of earth from sliding down from the upper layers and 

 sinking into the bore. The whole procedure is thus rendered doubt- 

 ful. It is, therefore, necessary to use a special instrument, a lock- 

 fast bore, provided at its lower end with a section having a mov- 

 able shell. This section remains covered during the rotations to 

 the right as the shell shifts. The closed bore can be lowered, 

 opened at any depth, filled with earth, closed again and drawn up 

 for bacteriological examination. 



This tool can be applied only within definite limits. Whenever 

 we endeavor to go down about 4 or 5 m. the ground resists the 

 bore so strongly, that soon very massive and unhandy inclosures 

 must be used, and a further advance will soon have to be aban- 

 doned. 



Unobjectionable results can only be expected, in anj" examina- 

 tion of the soil, when the samples obtained are transferred to the 

 artificial medium as quickly as possible. Otherwise, a consider- 

 able increase of the originally existing germs in the particles of 

 earth wi]l likewise prevent the discovery of the natural conditions. 



The bacteriological examination of the soil, is, therefore, as diffi- 

 cult as it is complicated, and the rarity with which it is undertaken 

 need not be wondered at, the less so because all the observations 

 hitherto made have led essentially to the same results, hardly re- 

 quiring continued examination. It has been ascertained that the 

 upper parts of the earth, almost everywhere, contain vast quan- 

 tities of diverse bacteria, partly of pathogenic nature (such as 

 oedema, tetanus, and anthrax bacilli), while the lower strata, even 

 those belonging to the region of underground water (unless forcibly 

 torn from their natural conditions by man), are wanting in or are 

 even free from bacteria. 



3. Investigation of Water. 



The method of bacteriological examination of water is almost 

 perfect. There is very little difficulty from the beginning and its 

 manipulation is exceedingly easy. Water is a substance of which 

 accurately-measured quantities can be taken and it is not difficult 

 to mix it so intimately and uniformly with the nourishing gelatin 

 that the germs are completely separated and without exception 

 develop into colonies. The latter will, therefore, both in number 

 and kind, correspond with the germs sown, and furnish perfectly 

 clear results. 



The objection that our nourishing gelatin does not supply the 

 conditions of growth for all the kinds of bacteria existing in the 

 water and that, therefore, the results must be unreliable, has al- 



