330 On Certain Bacteria from the Air of Neiv York City. 



Milk .30 cc. Acid. 



Reduction of Nitrate. 



As the rate of action of the culture on its medium depends a 

 good deal on the "dose," or the number of bacteria introduced 

 on the inoculation needle, the effect of this factor must be allowed 

 for. There is no way of regulating this adequate!}' ; but I think 

 the above table shows that there is individual variation in the 

 descendents of a single cell, apparent!}- independently of the en- 

 vironment. The number of the cultures practically eliminates the 

 effect of the dose, when we take an average of them. It will be 

 noticed that on the whole No. 10 i)roduces the most marked effect, 

 and No. 8 the least. 



I find that in taking cultures in the ordinary manner from one 

 tube to a new one by taking up a mass of growth on the needle, 



* Not planted at the same time as the others. 



