RECENT RESEARCHES INTO THE HISTORY OF BACTERIA. 261 



cocci ; when this has gone on for a certain time, micrococci 

 escape by the bursting of one side ; and the envelope which 

 is left is seen to have a double contour, and is easily recog- 

 nisable by its greenish-brown colour. One remarkable form 

 of this genus, which Billroth calls -(4. parvus, hsis been found 

 by him in water containing flesh ; it is a pale finely- 

 granulated ball, not unlike an unnucleated lymph-corpuscle, 

 which swims about by means of cilia, like the contractile 

 Myxomonads, and soon, developing long processes, comes to 

 resemble a Myxamoeba ; this form, however, Billroth regards 

 as the encysted spore of a Myxomycetes (perhaps JEtha- 

 lium septicum), while the microccoci within it have been 

 simply eaten ; if this be Ascoccocus — and Cohn thinks that it 

 is not a Bacterian form — it is clear that Billroth has described 

 two things under one name ; the other form Cohn has, how- 

 ever, found, and describes as Ascococcus Billrothii. 



2. This form he observed, not in putrescent fluids as did 

 Billroth, but by the examination of air collected by a new 

 process which he describes in this paper, and which is of 

 sufficient importance to detain us for a short time. Being 

 busied, he says, in the beginning of 1874, with the important 

 question, as to whether germs of Bacteria capable of develop- 

 ment under normal conditions are to be found in the air, 

 he invented — after rejecting the processes of Pasteur and 

 Pouchet — a method by which the Bacteria-germs, if present, 

 are passed through a solution in which they are able to de- 

 velope. Air was passed by means of an aspirator through a 

 series of wash-bottles, which were filled with twenty grammes 

 of his " normal fluid," the composition of which he gave in 

 his previous essay. Two large glass bottles, each of which 

 held ten litres, and which were made air-tight by bungs 

 served as the aspirator ; through each bung passed two glass 

 tubes, bent at right angles, one passing to the bottom of the 

 bottle, and the other reaching just below the bung; one 

 bottle then being filled with water, and placed at a higher 

 level than the other, and the tubes united by caoutchouc 

 piping, the desired current was produced. The upper bottle 

 was now united by caoutchouc piping to the series of wash- 

 bottles, and the air passed in, in bubbles. When the lower 

 bottle becomes full, it changes place with the upper; and this 

 change, with the consequent alteration of the piping, is the 

 only trouble to which the experimenter is put by this method; 

 while the volume of air which enters is easily known, as ten 

 litres are washed in each experiment. The importance of 

 this arrangement is, as Cohn points out, that the germs 

 develope, and the various species can be named macro- 



