APPENDIX. 233 



lus is said to have been detected in the breath of patients 

 suffering from phthisis. 



These points indicate that, in addition to the interest 

 for the microbiologist, considerable importance from a 

 hygienic point of view must be attached to the sys- 

 tematic examination of the air. Especially a knowledge 

 of the microbes which are found in the air of marshy and 

 other unhealthy districts, and in the air of towns, dwel- 

 lings, hospitals, workshops, factories, and mines, will be 

 of practical value. 



Miquel,* who has particularly studied the bacteria in the 

 air, has found that their number varies considerably. The 

 average number per cubic metre of air for the autumn 

 quarter at Montsouris is given as 142, winter quarter 49, 

 spring quarter 85, and summer quarter 105. In air col- 

 lected 2,000 to 4,000 metres above the sea-level, not a 

 single bacterium or fungus spore was furnished, while in 

 10 cubic metres of air from the Rue de Rivoli (Paris) 

 the number was computed at 55,000. 



The simplest method for examining the organisms in air 

 consists in exposing plates of glass or microscopic slides 

 coated with glycerine, or a mixture of glycerine and glucose 

 which is stable, colourless, and transparent. Nutrient 

 gelatine spread out on glass plates (p. 71) may be exposed 

 to the air for a certain time, and then put aside in damp 

 chambers for the colonies to develop. Sterilised potatoes 

 prepared in the usual way (p. 77) may be similarly exposed. 

 In both the last mentioned methods separate colonies 

 develop, which may be isolated as already described, and 

 pure cultivations carried on in various other nutrient media 

 (p. 74). Nutrient gelatine has also been employed in the 

 special methods of Koch and Hesse. 



Koch's Apparatus. This consists of a glass jar 

 about six inches high, the neck of which is plugged with 

 cotton wool. In the interior is a shallow glass capsule, 

 which can be removed by means of a brass lifter. The 



* Miquel, Organismes vivants de r atmosphere. 



