454 Transactions of the Society . 



patches made their appearance, and gradually coalescing, joined the 

 edge of the inoculation. Of their nature I can say nothing 

 definite. How they came there is rather puzzling, seeing none 

 formed in other parts of the jelly. 



At the same time, and in a similar manner, the same nutrient 

 medium was inoculated with a speck of the old pellicle from the 

 ice in the pan : the club-shaped rods did not, at this date and in 

 this medium, undergo any visible change ; but some of the minute 

 organisms showed development, though not to any great degree, only 

 exhibiting Brownian movement, whilst some of the same pellicle 

 placed on the boiled white of egg at the same time as the former 

 experiment with the pellicle from the hail, furnished on the second 

 day minute organisms which, when seen in a droplet of distilled 

 water, were not very active; but the club-shaped rods, if they multi- 

 plied, did so to an indiscernible extent. There was no chromo- 

 genous change at the point of inoculation, as with the pellicle from 

 hail. 



The minute organisms found in the melted hail-water scum, 

 were no doubt derived from the rain-drops congealing round the 

 air-borne dust-particles to which they were adherent, and after- 

 wards slowly multiplied afresh on the surface of the melted hail. 

 Some have doubted whether bacteria form part of the atmospheric 

 dust; but the very careful experiments and cultures of M. Miquel, 

 at the Montsouris Observatory, tend to prove that such bodies are 

 suspended in the air and to be constantly found in rain, hail, and 

 snow. Numerous figures are given. To avoid contamination in 

 culture experiments, when objects are only for a short time exposed 

 to unfiltered air, is a great source of difficulty. M. Miquel 

 remarks in the ' Annuaire,' published this year, that snow, usually 

 regarded as the great air-purifier, is not so in reality, for although 

 it largely attracts the bacteria it meets with in its passage, it does 

 not fix them like moistened earth ; as a sudden squall cutting into 

 the snow will often again bear them aloft. January and February 

 have furnished him with the minima ; October and November with 

 the maxima in the gatherings. Cold he places the first, and 

 extreme dryness the second agency in the destruction of atmo- 

 spheric bacteria. Kainfall much lessens their number, whilst this 

 again rises upon the succeeding dryness. He finds them ten times 

 more numerous in the centre of Paris than in the country, for the 

 same volume of air, and he gives the proportional numbers as, 

 micrococci 93, bacilli 5, bacteria 2, for the first, and micrococci 

 79, bacilli 14, bacteria 7, for the second. He also furnishes the 

 mean for the different months. The micrococci are pretty con- 

 stant, the bacilli highest in April, May, July, and August, and 

 lowest in November, January, and June ; the bacteria nil in 

 January, February, and June, and highest in the month of May. 



