SOURCES OF INFECTION. 31 



precipitation had been practised he always obtained numerous and 

 large colonies after exposure to the action of the antiseptic for 

 fifteen minutes, less after thirty minutes, and very few after an 

 hour's exposure, and only in exceptional cases were positive results 

 obtained after action of the antiseptic for two or three hours, and 

 with one exception never after seven to twenty-four hours' expo- 

 sure. Combinations with other antiseptics had no retarding effect. 

 From his experiments he was led to conclude that spores exposed 

 for some time to a sublimate solution will not grow upon a soil 

 containing the antiseptic in a very diluted form, while spores simi- 

 larly treated will not grow upon a soil upon which spores not so 

 treated will grow. 



By improved methods of investigation it has recently been made 

 possible not only to demonstrate the presence of microbes in the 

 atmospheric air, but also to prove their identity and approximately 

 to determine their number in a certain volume of air. From the inge- 

 nious experiment made by Miquel (" Des bacteries atmospheriques," 

 Comptes rend., t. 91, No. 1) it appears that the air picks up in its pas- 

 sage across the city of Paris in the course of half an hour three times 

 the number of microbes it contains when blowing over the country. 

 On the basis of a series of carefully-made observations to determine 

 the number of microbes which a certain volume of air contains at 

 different seasons of the year, he found that a cubic centimetre of 

 air contains on an average two hundred spores of bacteria. During 

 the summer such a volume of air often contains as many as 1000, 

 while during the cold months of winter it contains as few as 4 or 5. 

 In rooms with no draft of air, it required 30 to 50 litres of air 

 for a successful inoculation of a sterile culture substance. In 

 Miquel's laboratory 5 litres were found sufficient, while 1 litre of 

 air taken from the subterranean channels in Paris produced the 

 same effect. In a cubic yard of air taken from the wards of a long- 

 used hospital he found as many as 90,000 microbes. This same 

 observer has shown, and others have confirmed it, that sea air con- 

 tains scarcely any of these microorganisms, and that mountain 

 heights are as nearly free from them for obvious reasons. 



In a recent communication to the Royal Society, Dr. Frankland 

 described a new method of examining air for microorganisms. It 

 consists in aspirating a known volume of air through a glass tube 

 containing two sterile plugs of glass wool alone, or of glass wool 

 with fine glass powder, etc., the first plug being more pervious than 

 the second. These plugs are then transferred to sterilized liquid 

 gelatine-peptone, thoroughly agitated with it, and then the gelatine 

 is congealed, so as to form an even film over the inner surface of 

 the flask. The number of colonies which develop are then counted. 

 Klebs has devised a very ingenious but complicated apparatus for 



