58 BACTERIA. 



albuminoid matter floating in the atmosphere, as a result of 

 the vegetative power of which, organisms of various kinds, 

 according to the conditions by which these particles find 

 themselves surrounded, were caused to be developed. In 1854 

 Schroeder and Von Dusch made a great advance ; they proved 

 that simple filtration through a layer of cotton wool was 

 sufficient to deprive the air of its organisms, and so to render 

 it unfit to produce decomposition in infusions from which 

 germs had already been eliminated by heat ; and no longer 

 than thirty years ago Hoffmann, Chevreul and Pasteur 

 demonstrated that it was quite sufficient to draw out, and 

 bend downwards, the neck of a bottle in which the germ- 

 free infusion was contained, in order to ensure the 

 continuance of a non-putrefactive condition, and the 

 perfect freedom of the fluid contained within the flask 

 from germs : they argued that germs obey the law of 

 gravitation, like all other solid particles, when not blown 

 about by currents, and must settle down upon an upper 

 surface, so that when the tube was bent downwards the 

 organisms could not fall into the mouth. Tyndall gave 

 demonstrative proof of this in his exquisite experiment of 

 removing all particles from a glass chamber, first proving 

 their entire absence by passing through the chamber a ray 

 of light which could only be seen so long as particles 

 remained suspended in the atmosphere. As soon as the ray 

 of light disappeared from view he placed vegetable infusions 

 which had been sterilized by heat within the chamber, with 

 the result that they remained free from any trace of organic 

 life for several weeks together. Schwann had already pointed 

 out that blood, taken with certain precautions and introduced 

 into a flask in which the air was kept germ free, might be 

 preserved for a considerable length of time, without the 

 development of micro-organisms, and later (1857) Van der 

 Broek showed that the juice of grapes, and urine as well as 

 blood, might be kept free from decomposition and the 

 presence of organisms if the apparatus into which they were 

 received was first thoroughly sterilized by means of heat, 

 and if the substances were not allowed to come in contact 

 with the outside air. 



Numerous observers, especially Burdon Sanderson, Roberts, Lister, 

 Chiene and Ewart, and Watson Cheyne in this country, and Rindfleisch, 

 Klebs, Cazeneuve and Livon^Leube, Hauser and Marchand abroad, con- 



