OF OBTAINING LIVING PAETKLES FROM AIR. O' 



in fully formed tissues in every part of the body, and 

 may easily make theii' way along: the crevices between 

 protective epithelial cells into the tissues beneath, and 

 then thi-ough the thin walls of the smallest vessels 

 into the blood. 



»?. Of obtaining living particles from air. — Very 

 minute Hving particles may be obtained from the air 

 in many ways. Perhaps the simplest process is to 

 allow the vapour of the atmosphere to condense on 

 the sides of a perfectly clean glass vessel filled with 

 ice. The drops of water as they trickle down the 

 sides are to be received into a conical glass, and any 

 Hving particles entangled in the fluid can be detected 

 upon microscopical examination with a sufficiently 

 high power. In many instances two kinds of particles 

 will be found — one soft, exhibiting movements in the 

 fluid in which it is suspended; the other spherical or 

 oval in form, comparatively firm, and possessing con- 

 siderable resisting power. The first are often ex- 

 tremely minute, and so very transparent that th^y can 

 only be distinguished from the medium in which they 

 are suspended by very high magnifying powers, used 

 with the greatest care and under the most favourable 

 circumstances. 



8. Two kinds of matter in a living particle. — Fur- 

 ther examination enables us to demonstrate tliat the 

 particles last spoken of are composed of matter in 

 two difierent states : 1, a firm envelope closed at all 

 points ; and 2, a little delicate transparent matter 

 within this, and resemblins; the material of which the 

 first kind of particles seems to be entirely composed. 

 I shall presently endeavour to show that these cap- 

 suled particles of living matter were not always so 

 inclosed, and that the capsule was, in fact, formed iii 

 consequence of changes taking place upon the surface 

 of a particle of living matter like the particles first 

 referred to. 



9. Two kinds of living particles. — Living things 



