170 Royal Society: — 



examiuatiou of a simple infusion of new cheese taken by itself) 

 adds a considerable number of highly refriugent spherules of various 

 sizes (oil-globules) and finely granular flakes, also a few Bacteria 

 and (if the cheese be not quite new, almost certainly) fungus-myce- 

 lium and conidia in quantity. 



Fresh-boiled turnip-infusion alone ma}"- contain so very few 

 dead Bacteria that none are detected with the microscope, or only 

 one in a drop. It presents a great number of minute, highly re- 

 friugent spherules, varying in size from -jnhjJi ^^^^^ downwards, all 

 in most active oscillatory movement. Shreds and filaments of 

 various sizes and character also are found, and a few finely 

 granular flakes about j-^-^o ^^^ ^ diameter. The addition of 

 cheese brings in, of course, the objects enumerated above as 

 belonging to it. 



Visihility of Bacteria. — It is perhaps necessary to say, before 

 proceeding further, that we have satisfied ourselves that, iu infu- 

 sions of the optical character of those used, the multiphcation of 

 Bacteria makes itself obvious by a cloudiness. Hence, though we 

 have not remained content ^A"ith that evidence, the retention by' 

 such a Kmpid infusion of its limpidity is a proof of the absence of 

 Bacteria. We also should mention, what is aacU kno«Ti already, 

 that in a closed tube or bottle, after such a cloud (of Bacteria) has 

 developed, the Bacteria at a certain period cease to midtiply and 

 settle down as a fine powder, leaving the fluid agaia clear. Such 

 precipitated Bacteria remain unchanged in the fluid for a long 

 period (weeks certainly, perhaps years), and can be readily shaken 

 up and at once recognized by microscopic examination ; they are, 

 moreover, not destroyed by boUing : hence it is not possible to 

 miss the detection of a development of Bacteria in a limpid turnip- 

 infusion, examined daily for three weeks or more by the naked 

 eye, and finally, after agitation, by means of the microscope. 



Series A. K^ov. 23rd. Experimeats with hay-infusion. — An in- 

 fusion was prepared by pouring water of about 90° C. on to 

 chopped hay. The infusion -^'as of a dark sherry-colour ; reaction 

 slightly acid. The glass tubes used in this and subsequent experi- 

 ments were about five inches iu length, of half inch bore, rounded 

 at one end and drawn out to a capillary orifice at the other. 

 The infusion in these and subsequent experiments was introduced 

 by heating the tube and plunging its capillary beak beneath the 

 surface of the experimental liquid during the cooling of the expanded 

 air, until the tube was about one third or half filled. Tubes 1, 

 2, 3 were half filled vdth the hay-infusion previously filtered, the 

 liquid was boiled in the tube, and the capilkiry beak fused, as neai'ly 

 as possible, during ebullition *. 



* The tubes were sealed at the moment of removal from the flame over which 

 they had been boiling. In every ease a subsequent recurrence of ebullition 

 was observed during the cooling of the upper part of the tube. Dr. Roberts, 

 of Manchester, has suggested that the occurrence of Bacteria in tubes thus 

 sealed may be explained by their in-drauglit, together with a certain amount 

 of air, at the moment of closure; but the experiments of Sanderson, recently 

 confirmed by Cohn, have shown that contamination of thuds by Bacteria only 

 takes place through the medimn of impure surfaces or liquids. 



