Page:Popular Science Monthly Volume 73.djvu/162

158 a glass jar to avoid contamination from the air. In order to estimate the number of bacteria present, 0.5 c.c. of this wash water were diluted with 10 c.c. of physiological salt solution and three series of agar plates were poured, using 0.2, 0.3 and 0.5 c.c. of this dilution. The wash fluid was then measured and centrifugated, the coarse particles of dirt and paper thus thrown down were filtered off and the fluid again centrifugated. With the sediment of bacteria and fine dirt obtained in this manner, I inoculated three bouillon tubes in order to look for streptococci and other forms that might develop. Ten tubes of serum were smeared for the detection of Bacillus diphtheriœ, while the rest of the sediment was then carefully injected subcutaneously into a guinea pig. The animals were closely observed for several days so that in case of a fatality an autopsy could be performed immediately after death and the lesions thus more correctly observed. All media used for this experiment were prepared according to the standard method of the American Public Health Association, with a final reaction of +0.8 (0.8 per cent. acid).

At first I intended to make a study of only twelve bills, since it required a full week to complete the study of each bill; but the appearance in the daily press of accounts of the present agitation for clean money led me to make a total of twenty-four examinations. In twenty of these all the sediment was injected into guinea pigs, in order to allow the development of tuberculosis or septicæmias that might be caused by the bacteria in the sediment; in the other four, the sediment was used for smearing serum plates to detect Bacillus diphtheria.

It was surprising to find the flora so constant, Staphylococcus pyogenes alius being by far the most common form present, with various members of the subtilis group next; Staphylococcus pyogenes aureus was found on all bills, but not in large numbers. The following were found on some bills, but always few in number; Staphylococcus cereus albus, a streptothrix, Sarcina lutea, streptococci and in one instance, Bacillus xerosis. Other chromogenic bacteria were frequently found but not identified.

The numbers of bacteria present on the bills ranged from 14,000 up to 586,000, with an average for twenty-one bills of 142,000. There seemed to be no connection between the amount of dirt and the number of bacteria present; the cleanest-looking bill that I used had next to the highest count (405,000), while the bill that looked the dirtiest had but 38,000. When a bill has been in circulation for a short time and has become somewhat cracked, and its peculiar glaze worn off, the bacteria very easily cling to it without the presence of dirt and grease.

All inoculations gave negative results, the time limit being placed at from six to seven weeks. All of the guinea pigs showed more or less local reaction, with swelling of the lymph glands of the groin, but