Colonies for a Satisfactory Soil Plate. 95 
_of growth rather than stop the growth of any individual organism. 
With mixed cultures the media may be suitable for the growth of all 
the organisms present, but the differences in rate of growth and specific 
end products cause uneven plates. (See Plate I.) 
The literature does not furnish figures on duplicate and triplicate 
platings where the bacterial dilutions were made from large aliquots 
(10 ce. or more). In milk it has been noted that platings giving as low 
as forty colonies are satisfactory.” The soil is so much more ununiform 
than milk that the technic worked out at this station,’ and depending 
on large aliquots for diluting and plating, was followed. 
EXPERIMENTAL WORK. 
A black sandy soil was air dried and sieved to unify both the soil 
and its flora. Triplicate platings were made from 1-40, 1-400, 1—4,000, 
1—-40,000 and 1-—400,000 bacterial dilutions. Counts were made after 
three, seven and ten days’ incubation at 20° Centigrade. Especial care 
was taken in handling the plates to prevent contaminations. The check 
plates were in most cases entirely free from bacterial growth and their 
average has been deducted from the figures given. The results are 
given in Table I. 
2Conn, H. W. Public Health Reports. U. S. Publie Health Service, Vol. 30, No. 33, 
August, 1915. 
3 Noyes, H. A., and Voigt, Edwin, in Proceedings of Indiana Academy of Science, 
1916, pp. 272-301. 
