158 PRACTICAL BACTERIOLOGY. 



water sliould reach the warm portion. The tube 

 would be sure to crack if either of these precautions 

 were neglected, and even if the crack were too small 

 to be seen at oncej it would be sure to cause the 

 destruction of the tube during transportation. 



If the interval between the taking of the samples 

 and their examination is to be short, the test-tubes 

 may be taken away simply packed in a small box. If, 

 however, the examination is to be very exhaustive, and 

 an interval of several hours or even days must elapse 

 before it can take place, the sample must be protected 

 in a special manner against the influence of time and 

 of the altered outward conditions in which the bacteria 

 find themselves. It must be taken as a general rule 

 that the bacteria, if left to themselves, multiply rapidly 

 in the sample, so that after a lapse of several hours 

 there are sure to be many more germs in proportion 

 in the sample than there were originally in the water 

 of the well, and on that account the judgment formed 

 of the water, if it rested principally on the number of 

 germs the sample contains, would be quite incorrect. 

 There is, however, a way to prevent this multiplication 

 of the bacteria, that is, by keeping the tubes suffi- 

 ciently cool. If the temperature sinks below a certain 

 point, although the vitality of the bacteria remains 

 unaffected, no division occurs with most species, whilst 

 with the remainder it only takes place very slowly. 

 This temperature varies with different species, but we 



