22 OF DETECTING GERMS 



velope of formed material, it is able to resist effectually 

 and for a long time the disturbing influence of adverse 

 external conditions. Should these lead to the death 

 of a great part of the living matter or bioplasm, it 

 must be remembered that by. this very change, the 

 thickness of the external envelope is increased, and 

 thus the speck of living matter which remains, be- 

 comes still more effectually protected than it was at 

 first (see Figs. 9 and 10, plate II.). 



Protected in this way, multitudes of such germs 

 escape destruction. Provided only a speck of living 

 matter remains, and resists the influence of adverse con- 

 ditions, it will increase undei favourable circumstances. 

 Particles will make their way through pores in the 

 envelope, and coming into contact with the pabulum 

 outside will soon increase and develope minute germs 

 or branching stems as represented in Figs, n and 12. 



Of the Detection of Vegetable Germs in the Air. 

 Vegetable germs were detected in the air more 

 then twenty years ago by a number of observers, and 

 by many different plans of procedure. One method 

 was to cause air to be drawn through a glass vessel, 

 the outside of which was cooled by ice. Upon collect- 

 ing the water which condensed upon the interior in a 

 vessel placed beneath for its reception, and examining 

 under the microscope the slight sediment which sub- 

 sided, the germs were discovered. Another plan was 

 to cause air to be projected against glass plates, the 

 surface of which had been wetted with weak glycerine, 



