KECENT RESEARCHES INTO THE HISTORY OF BACTERIA. 263 



unless they fall on a dirty surface, and are wetted there ; as 

 Cohn points out, these observations agree with those of 

 Burdon Sanderson, although he is convinced that, when 

 Bacteria did appear in the aspirator-bottles, thej were really 

 brought in by the bubbles of air, and washed out from them, 

 and that their presence was not to be ascribed to any chance 

 contact of surfaces. 



3. Imbedded in a fluid which also contained Micrococcus 

 crepusculum, Cohn found aggregations of varying size more 

 or less circular in form, which, with their surrounding mem- 

 brane, closely resembled frog's ova ; oae or more new aggre- 

 gations were found in one membrane, the smaller circular, 

 the larger irregularly elliptical ; the latter formed a '* carti- 

 laginous " corpuscle, which was with great difficulty broken by 

 pressure, not dissolved by ammonia, or coloured by iodine ; 

 but within them he found an aggregation of much smaller 

 bodies of circular form, capable of being stained yellow 

 with iodine, which were united together by a remarkably 

 firm intercellular substance, and surrounded by a very thick 

 cartilaginous envelope. These fresh characters are those of 

 the genus Ascococcus. The cell-families thus formed break 

 up into " nests " of irregular form, which are further divided 

 into lobes, which are again subdivided into lobules, giving, in 

 this way, to the whole the appearance of a bunch of grapes. 

 Their development takes place in the following manner: small 

 families of Micrococci are pushed towards the periphery of 

 the surrounding gelatinous membrane, increase enormously, 

 and thus get closely applied to one another ; the gelatinous 

 membrane grows at the same time; branches then appear, 

 and the whole takes on a knobbed or iregularly bunch-like 

 appearance ; the larger lobes are, by further division, broken 

 up into smaller ones, the membrane still embracing the 

 whole family ; but this separates the lobes when they grow 

 too large, and produces forms of the appearance represented 

 in figs. 4 and 5 ; and thus at last there are produced families 

 of Ascococci, which, at first small and circular, become 

 gradually larger, till they reach the stage represented in 



fig- 3.1 



The chemical activity of this form is very remarkable ; 

 thus, it gives rise to a peculiar milky or cheesy odour, 

 arising, as Cohn thinks, from the production of lactic acid, 

 and lactic ether from ammonium tartate ; and, further, the 

 originally acid reaction of the nutrient solution is changed 



' These numbers refer to Cohn's figures. Fig. 1 of our plate gives a 

 good idea of the general appearance. 



