Blasius.] bbo [13ee. 17, 



in certain localities, particularly in large cities. The most wonderful 

 discoveries have been made in this direction by Ehrenberg, Schroeder, 

 Pasteur, Dr. Saaitli, Schwann, Cohn, Dr. Bastian, Tyndill, Pettenkofer, 

 aud others. 



Schroeder succeeded first in filtrating air by letting it pass through 

 chemically pure cotton into a glass cylhider, from which the air had been 

 exhausted by an air-pump. 



The eminent French chemist, Pasteur, by using chemically pure gun 

 cotton, which he, after the filtration, dissolved in ether, succeeded in 

 ollecting all impurities of the filtrated air, and subjecting the fluid to a 

 microscopic investigation, he observed myriads of fungi and still smaller 

 living organisms as Bacteria and Vibriones in it. He says: "It appears 

 that our knowledge of contagious diseases, especially at periods when 

 epidemics rage, would be increased by work carried out in this direction." 

 Following his own suggestions, he was enabled to prescribe a means of 

 jireventing the disease known as "pebrine," which made such havoc 

 amongst the silkworms in France. 



Schwann showed that a fluid which produced myriads of such lower 

 living organisms if left in contact with ordinary air, would keep free of 

 them if first boiled and then brought in contact with air pi'eviously 

 heated to redness ; proving thus clearly that the germs of life came from 

 the air. It also was proved that meat, fruit, etc., will pi-eserve in pure air 

 from one to two years and that fermentation and decomposition is carried 

 on by the assistance of such minute organisms in the air. The conclu- 

 sions, then, are not so far off fi-om the truth that such minute parasites 

 if in sufficient numbers, may, in entering on the wings of the air into 

 our system, attack delicate or diseased organs, producing fevers, such as 

 diphtheria, scarlet fevex", etc. In the fall and spring, the times of sudden 

 weather changes, we see an ordinary cold or catarrh in children change 

 frequently into diphtheria, or other similar diseases. 



Blackley considers he has proved that hay fever is caused by the in- 

 halation of air containing pollen in considerable quantity, which adheres 

 to the membranous lining of the larynx and air-passage and causes secre- 

 tion from these parts. A solution of quinine, which is destructive to 

 minute forms of life, has been shown by Ilelmholtz to be an effective ap- 

 plication in cases of this disagreeable malady. 



Tyndall, in 1870, gave us a means of investigation supplementary to 

 the microscope, and of extreme delicacy. He proved that particles, 

 which in a liquid are quite invisible under an object glass readily show- 

 ing bodies of too^doo of an inch in diameter, were revealed with greatest 

 ease by means of a beam of light. If the air were pure, a beam of sun- 

 light traversing a darkened room would be invisible except where it 

 struck upon the wall. The scattering of the light by floating dust and 

 living organisms makes the track luminous to the naked eye. We may, 

 to a certain extent, see these impurities dancing in a beam of light 

 which enters through the shutters into a darkened room. 



