912 



SCIENCE. 



[N. S. Vol. XIL No. 311. 



the largest laboratories the quantity is 5 

 cubic centimeters. For results to be ob- 

 tained after four or more days of cultiva- 

 tion, the larger quantity is doubtless pref- 

 erable. For results to be obtained after 

 two days' growth, 5 cubic centimeters are 

 found to be more satisfactory. 



Practice varies with reference to mixing 

 the water and the gelatine in the tube or on 

 the dish, in those cases where Petri dishes 

 are used. There is no evidence to indicate 

 that this is a point of much practical sig- 

 nificance, affecting results beyond the or- 

 dinary limits of accuracy. 



With regard to standard conditions of 

 cultivation, the best available evidence 

 shows that it should take place in the dark 

 and in an atmosphere in which moisture 

 and oxygen are always present. Petri 

 dishes sometimes fit too tightly to give sat- 

 isfactory results, and special attention is 

 necessary to these particulars. The tem- 

 perature of cultivation should be uniformly 

 20 degrees C, and it is gratifying to note 

 that in mauy laboratories this standard has 

 been adopted, notwithstanding the care and 

 expense which it sometimes involves. 



The period of cultivation still varies 

 considerably in the difi"erent laboratories. 

 There is a well-defiued movement, how- 

 ever, toward shorter periods in order to se- 

 cure greater practical value for the data. 

 These practical advantages outweigh the 

 smaller numbers obtained from a shorter 

 period, especially as all results have only a 

 relative and not an absolute value. In 

 Germany 48 hours is the standard period 

 of cultivation, and daily results have been 

 obtained on this basis from each of 26 water 

 purification plants in operation in that 

 country. There seems to be no good reason 

 why the bacterial results to be obtained 

 from the various water purification plants 

 now in operation and about to be built in 

 this country should not be comparable with 

 those obtained abroad. This is especially 



true in view of the growing appreciation of 

 the fact that the residual numbers of bac- 

 teria in a filtered water should receive at- 

 tention as well as the percentage of bacterial 

 removal. Taking everything into consider- 

 ation, it would appear to your Committee 

 to be advisable to adopt 48 hours as a 

 standard period of cultivation under the 

 conditions noted above. Before making a 

 final recommendation there is requested a 

 further expression of opinion on the part of 

 the members of the Section of Bacteriology 

 and Chemistry. 



Relative to the records of the numbers of 

 bacteria per cubic centimeter, there are 

 many workers whose custom is very loose 

 and unscientific. Your Committee disap- 

 proves of customs which indicate a fictitious 

 accuracy in current methods, by the inex- 

 cusable use of significant figures in the units 

 place where the numbers are very high. 



Differentiation and Classification of Species of 

 Bacteria. — This branch of bacteriology is of 

 much importance in connection with water 

 analysis, because reliable and readily avail- 

 able methods for the detection of water- 

 borne disease germs cannot be established 

 until this general subject has been placed 

 upon a more scientific and substantial 

 basis. It is true, of course, that progress 

 for a time along this line must be largely a 

 matter of pure science, and that interest in 

 these developments is shared not only 

 among water analysts, but all workers in 

 applied bacteriology. 



Your Committee has made every reason- 

 able effort to secure a consensus of opinion 

 as to how this subject now stands, with ref- 

 erence to the soundness or weakness of the 

 various current methods and procedures. 

 While the views of a number of prominent 

 workers, especially those not directly con- 

 nected with water analysis, have not yet 

 come to hand, it is believed that the gea- 

 eral status of affairs may be correctly out- 

 lined as follows : 



