226 ON RECENT IMPROVEMENTS IN THE 



be pretty safely assumed from analogy, if it were granted that they are living 

 organisms ; though, indeed, I once heard it propounded in conversation by 

 a very sound and eminent chemist that, for aught we could tell to the contrary 

 living matter in its lowest forms might exist in a soluble condition — an idea 

 suggested by Dr. Sanderson's statement that a drop of water in which no 

 bacteria could be discovered by the microscope will nevertheless give rise to 

 the development of such organisms when added to a liquid adapted for their 

 growth. But those who hold that the septic agents are not organisms at all, 

 but so-called chemical ferments, might with greater justice contend for their 

 possible solubility. The point being of great practical as well as speculative 

 interest, I have been glad to obtain conclusive evidence regarding it from some 

 simple experiments lately performed, and hitherto unpublished. I must content 

 myself on the present occasion with briefly indicating their character. 



A series of experimental glasses, contrived so that their contents shall be 

 securely protected from dust, though the atmospheric gases gain free access 

 to them, having been purified by heat, are charged with some liquid, like boiled 

 milk, favourable for organic development and prone to fermentative changes, 

 but uncontaminated at the outset by the presence of any living organism.^ If 

 the glasses so arranged are left undisturbed, the liquid remains unaltered for 

 an indefinite period, except that its bulk is slowly diminished by evaporation. 

 But if a minim of ordinary drinking-water is added to any one of the glasses, 

 its contents will in a few days be obviously altered in chemical character, and 

 before long will probably be decidedly putrid, the microscope at the same time 

 revealing abounding bacteria — a result in perfect accordance with Dr. Sander- 

 son's observations. If, however, instead of an entire minim, a small portion 

 (say a hundredth) of a minim of the same water is added to each of a series 

 (say ten) of such glasses (which can be readily done by means of a small syringe,^ 

 having its piston-rod in the form of a fine-threaded screw, on which a graduated 

 disc revolves to regulate the amount of liquid emitted from the slender glass 

 tube that constitutes the nozzle of the instrument), a very different result ensues. 

 Some of the glasses probably remain permanently unchanged, as if nothing 

 had been added to them ; and those which do experience alteration show plainly, 

 by differences of colour and of smell, that they are undergoing various kinds 

 of fermentation, while the microscope shows corresponding differences in the 

 characters of the bacteria found in them. 



It is hardly needful to remark that if the ferments were dissolved in the 



^ For an account of the manner in which these conditions are fulfilled see a paper by the author 

 entitled ' A further Contribution to the Natural History of Bacteria ', &c. (Microscopical Journal, 

 October 1873). (See vol. i, p. 309.) ^ See vol. i, pp. 364-5. 



