THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. YII. 



Washington, D. C, April, 1886. 



No. 4. 



Notes on the Biological Examina- 

 tion of Water, with a few Sta- 

 tistics of Potomac Drinking 

 Water.* 



BY THEOBALD SMITH, M. D. 



It is well known that micro-organ- 

 isms belonging to the class bacteria 

 or schizomycetes are incapable of 

 being nourished by inorganic sub- 

 stances alone ; they require, in addi- 

 tion to certain inorganic salts, sub- 

 stances derived from animal and 

 vegetable organisms. According to 

 Niigeli the nitrogen is obtained from 

 compounds having the structure of 

 amides and amines, the carbon from 

 compounds which contain the group 

 CH3 or CH. 



From this it follows that the more 

 bacteria a certain quantity of water 

 contains, other conditions remain- 

 ing the same, I the more organic mat- 

 ter it holds in solution or suspension. 

 To determine the number and kinds 

 of bacteria which a given water con- 

 tains has been of late termed the bio- 

 logical analysis of water. Dr. R. Koch 

 was the first to suggest and apply 

 this biological test to drinking water. 

 The enumeration of bacteria was only 

 made practicable by his method of 

 gelatin plate cultures, as the elabor- 

 ate and tedious j^i'ocesses of Miquel, 

 Fol, and others by means of liquid 

 cultures in tubes can never become 

 generally useful. 



♦Abstract of a communication presented to the Uio- 

 logical Society of Washington, March 20th, 1886. 



fThis limitation must always be borne in mind. 

 Thus distilled water, from which small quantities were 

 occasionally siphoned out, kept in the laboratory un- 

 disturbed for one or two months, contaiiied 18,750 

 bacteria in i c.c One month later the same water con- 

 tained 41,512 in 1 c.c. If distilled water can sustain 

 such a large number of germs the number which 

 natural waters would contain under like circum- 

 stances must be enormous. 



The method consists briefly in add- 

 ing to a quantity of sterilized nutritive 

 gelatin, liquified by gentle heat, a 

 certain quantity of the water to be 

 tested, thoroughly mixing the two, 

 and pouring the mixture u2:)on a glass 

 plate where it rapidly solidifies. The 

 individual micro-organisms are thus 

 separated from one another ; each 

 multiplies into a colony, which be- 

 comes visible to the naked eve in one 

 to three days, and each colony, the 

 progeny of the germ originally sown, 

 is therefore to be counted as one. 

 Finally, it is customary to calculate 

 from the results obtained the number 

 of germs in i c.c. 



The quantity of water to be taken 

 depends on the number of bacteria 

 probably present, and must be so 

 chosen that this number is conve- 

 niently and correctly estimated. 



An important fact in connection 

 with this mode of analysis is the rapid 

 multiplication of germs in water after 

 it has been kept in tubes or bottles at 

 the ordinary temperature of a room 

 for a short time. A specimen of 

 water containing about 3,000 germs 

 at the time it was collected, when 

 kept in the laboratory one day, con- 

 tained at least 60,000 germs. Several 

 causes may be assigned for this in- 

 crease • I. There may be some or- 

 ganic residue in the collecting tubes 

 which has survived a temperature of 

 i5o°-i7o° C, to which they are ex- 

 posed for the purpose of sterilization. 

 This source of error may, I think, be 

 avoided by thoroughly flaming the 

 collecting tube before use. It seems 

 reasonable to suppose that by this 

 means all organic compounds will be 

 broken up. 2. Natural watei^s usually 



