263 p. JEFFREY BELL. 



scopically, while with the ordinary methods of examination of 

 air it is impossible to do this, as the spores or germs are only 

 seen, as such, and that by the aid of the microscope. 



As precautionary measures, all the glass vessels used must 

 be boiled for a lor^g time in the water bath ; corks are to be 

 avoided, as they shelter spores in their cracks, and glass 

 stoppers or gutta percha used in their place ; and, lastly, the 

 connection of the vessels which contain the nutrient solution 

 must be so arranged, that no entrance of spores is possible 

 after they have been boiled. 



The passage of the air bubbles was regulated by a clip 

 placed on the tubing, so that the ten litres of air took one to 

 two hours in passing over. Notwithstanding this precaution 

 an uncertain quantity of sjjores passed, apparently carried by 

 the air bubbles, through the washbottles. After a certain 

 quantity of air had been " sucked through," a precipitate or 

 a troubling of the contained water was observed in these 

 washbottles ; white clouds of mycelium were, in all cases, 

 observed on their walls and bottoms, which grew rapidly, and 

 were easily seen by the naked eye ; while on the surface of the 

 nutrient fluid the mycelia fructified, and often allowed Cohn 

 to see their hyphee bearing the conidia. To hasten develop- 

 ment he was in the habit of placing the washbottles, after a 

 time, in his warm chamber (described Heft II, p. 196) at a 

 temperature of 30° C. In one bottle he placed Pasteur's so- 

 lution (with sugar), and in the other the normal Bacteria 

 solution (without sugar). He always found Aspergillus and 

 Penicilliwn ; which he was able to distinguish from each 

 other, by the loose character of the mycelium of the former. 

 Mucor was found only once. On the natural assumption 

 that each growth developed from one spore, Cohn finds that 

 one such, capable of development, was obtained in every ten 

 litres of air ; and concludes from this that a man takes in 

 1000 such everyday, of which, of course, the greater number 

 are again passed out in expiration, or are in some way pre- 

 vented from developing. 



The cloudy appearance of the fluids was largely due to 

 circular Torula cells, united in couples ; the oval smaller form 

 was rare ; in the precipitate were found smut and other 

 fungus-spores. " As a rule no Bacteria were developed in the 

 fluids of the washbottles ;'^ because, as Cohn thinks, they were 

 with difficulty held back by the water, and rather passed 

 over in the air bubbles without being wetted, as is the case 

 with the spores of Lycopodium (Heft II, p. 189) ; he sup- 

 poses, in effect, that they can only develope when thoroughly 

 wetted through, — a condition which does not easily obtain, 



