AIR. 



[ 20 ] 



AIR. 



This theory has now ceased to be acknow- 

 ledged; and a common source of fallacious 

 reasoning lies in overlooking the fact, that 

 the air contains the germs of numerous 

 animal forms, still capable of resuming their 

 active vitality when they meet with the 

 requisite conditions. Of this we have con- 

 vincing proof. For, if the hquid containing 

 the decomposing matters be heated to ebul- 

 lition for some time in a bottle or other 

 vessel, into the cork closing which two bent 

 tubes are inserted, and after the air has been 

 completely displaced by the vapom', the fresh 

 air admitted be previously passed through 

 red-hot tubes, which we have no reason to 

 believe exerts any action upon it, animalcules 

 cease to be met with, and the decomposition 

 of the substance and growth of the organisms 

 no longer take place, even for an indefinite 

 period. That the liquidin these cases does not 

 experience alteration rendering it incapable 

 of supporting the life of the animal forms 

 introduced, is shown by subsequently admit- 

 ting air which has not been heated to red- 

 ness, when the animalcules appear as rapidly 

 as in fresh liquids. 



In the infusoria, which are the forms most 

 frequently met with in infusions of decaying 

 substances, and the increase of which takes 

 place in a threefold manner, by subdivision, 

 gemmation, and the formation of ova, we 

 cannot wonder that these reproductive parts 

 are not frequently recognizable, when we 

 recollect that the perfect organisms them- 

 selves, in many cases, are barely within the 

 reach of the highest powers of our micro- 

 scopes. 



A list of the animalcules most commonly 

 existing in, or conveyed by the air, will be 

 given under the head of those liquids in 

 which we find them living : see also the 

 articles Infusions, Solutions, Fermen- 

 tation, and Putrefaction. 



Vegetable forms are constantly met with 

 as deposited from the air. In them, the 

 spores are probably alone the bodies by means 

 of which the diffusion of the lower plants by 

 the agency of the air is efi^ected. Minute 

 fungi are frequently found, like the animal- 

 cules above alluded to, in various vegetable 

 and animal hquids undergoing fermentation 

 and decomposition. The question of the 

 relation of these fungi to the processes, will be 

 found discussed under Fermentation and 

 Putrefaction; and the various genera and 

 species found in different kinds of liquids 

 are treated of under the heads of these 

 liquids. Fungi and algae are also met with 



as parasites and entophytes upon and in 

 living animals ; for an account of these, see 

 Parasites and Entophytes. 



The lower forms of fungi are frequently 

 found growing upon surfaces from which 

 they can derive no nourishment, as upon 

 slips of glass, \Aindow-panes, &c. In these 

 cases they must derive their nourishment 

 from the atmosphere. When found in these 

 situations, however, they soon cease to grow 

 by subdivision of cells or gemmation, but 

 sjieedily form spores. The most common 

 ones in these situations are the sugar fungus, 

 Penicillium glaucum and Aspergillus penicil- 

 latus, Mucors, &c. 



The method of distinguishing whether any 

 minute particle deposited from the air is of 

 animal or vegetable nature, is described 

 under Tissues, Animal and Vegetable. 



Organic bodies derived from the air are 

 sometimes met \Adth in snow and hail. 

 These are alluded to in the articles Snovvt 

 and Hail. 



The air has frequently been examined in 

 regard to the presence of animal or vegetable 

 organisms, which might account for the pro- 

 duction of epidemic and infectious diseases. 

 In none of these cases have any bodies ever 

 been found which could in any way be inter- 

 preted as the origin of the diseases — nothing 

 more has been met with than common infu- 

 soria and such other bodies as may at all 

 times be found in air, from whatever soiu'ce. 

 As these experiments cannot, however, be 

 too frequently repeated, it may be well to 

 point out the method of making them. The 

 best plan is to connect a glass tube, twice 

 bent at right angles, with an aspirator ; the 

 free end of the tube should be di'a\Mi to a 

 fine point, and just above this, the tube 

 should be blovATi into a bulb. The point is 

 then immersed in a small quantity of pure 

 water, and the water allowed to run very 

 slowly from the aspirator. The water is then 

 slowly drawn into the tube and the air is 

 washed as it passes b}' the water in the bulb. 

 When a large quantity of air has been 

 washed by the water, the latter is shaken 

 briskly and allowed to run into a clean glass 

 for examination. 



Another method consists in closing, by 

 fusion, the end of a glass funnel, filling 

 this with ice, and collecting the di-ops of 

 water condensed from the air in a receptacle 

 l^laced beneath. 



The appearances presented by air as exist- 

 mg in cell-cavities is represented in PI. 38. 

 fig. 23 a ; as confined in spiral vessels in 



