HYGIENIC LABORATORY METHOD 153 
TasBLte XI[—Contznued 
(FOR DILUTIONS)—STOCK 1 PER CENT SOLUTION 
[1 ec Disinfectant+99 ce Distilled Water =Solution B] 
cc ce ce ec cece a 43 
of dist of dist of dist 
B water B water B water 
1:1800= 5 + 85or 4 -+ 68 or2 + 34 
1:2000= 5 + 950r 4 + 76 or2 + 38 
1:2200= 5 + 1050r 4 + 8&4 or2 + 42 
1:2400= 5 + I115or 4 + 92 or2 + 46 
1:2600= 5 + 1250r 4 + 100 or2 + 50 
1:2800= 5 + 1350r 4 + 108 or2 + 54 
1:3000= 5 + 1450r 4 + 116 or2 + 58 
1:3200= 5 + 1550r 4 + 124 or2 + 62 
Subculture Tube Racks. Wooden racks, with 5 rows of 14 holes 
each, are used for holding the subculture tubes, and as plants are made 
from each mixture of culture and disinfectant every 25 minutes up 
to fifteen minutes, 6 tubes are required for each dilution. ‘Thus, in 
each rack we have 10 rows of 6 tubes each with 2 empty cross rows of 
VES fe liana ne aan ° 
i i i i 
—. 4 hal | : 
Fig, 43.—Block for Subculture Tubes. 
holes remaining, which are utilized by placing over in the next row each 
tube as it is planted. This makes it easy to keep run of the tubes that 
are planted. It is well also always to plant from the seeding tube in a 
certain hole in the water bath into a certain row of tubes in the rack. 
This, after a little practice, will help to avoid errors in planting. 
Method of Conducting the Test. If there are in one experiment 
more than 10 dilutions of the disinfectant, including the phenol controls, 
the stronger solutions of the disinfectant and phenol are tested first, 
as it will not be necessary to plant them after seven and a half minutes. 
The weaker solutions are then immediately done and are then planted 
every two and a half minutes for fifteen minutes. 
For keeping the time a stop watch can be used, but an ordinary 
watch will serve the same purpose by simply starting on the two-and- 
one-half- or five-minute periods. 
