CHANGES IN SMALL MASSES IN ZOOGLCEA 183 



different periods, the scum or pellicle that forms on such fluids. 

 What I have now to say will refer almost exclusively to infusions 

 made from hay. The hay employed may be either fresh or old, 

 but it does not do to substitute for hay mere unripe grasses. 

 I have elsewhere shown how remarkably different are the products 

 derivable from living, unripe grasses and from ordinary hay.' 



In making such an infusion I have been accustomed to cut the 

 hay into short pieces, to place these in a little beaker, and then to 

 add water so as well to cover the fragments. After maceration for 

 three or four hours at a temperature of about 86° F. (30° C), the 

 infusion has been filtered through two layers of the finest Swedish 

 filtering paper into another small beaker. In this way all but the 

 smallest particles, 1/15,000 of an inch or thereabout, will be ex- 

 cluded. For observation of the changes now to be described it is 

 best that the bacterial scum, which soon forms on the surface of 

 the fluid, should be very thin, therefore the infusion should not be 

 too strong, and the depth of the fluid ought not to be more than 

 about one inch. 



As all the processes with which we are concerned go on almost, 

 if not quite, as well in the dark as in the light, one simple plan is 

 to filter the infusion into small one-ounce earthenware pots, over 

 which the covers are then placed till the time comes for the 

 examination of their contents. If three or four pots are charged at 

 the same time, they may be opened at will on successive days, or 

 some may be exposed to one temperature and some to another. 



Otherwise the infusion may be left in a shallow open glass 

 vessel, exposed to light, and beneath a bell jar so as to exclude 

 dust. About 65° F. (18° C.) is a favourable temperature, and, when 

 thus exposed, in about twelve hours or so the fluid begins to show 

 slight turbidity, and as this increases the light sherry-coloured fluid 

 becomes gradually paler. In from twenty-four to thirty hours 

 a thin almost invisible scum will have formed upon the surface of 

 the infusion, often in the form of a coherent elastic membrane, and, 

 somewhere between thirty and forty hours, multitudes of small 

 zooglceal masses, such as I formerly termed "embryonal areas," of 

 varying size and shape will have formed, and will be found to be 

 imbedded in this thin scum or pellicle. These go on increasing in 

 size and growing in number till at last they may occupy more than 

 one-half of the pellicle. Fig. 10, A ( X 100) shows such masses, more 



■ " Studies in Heterogenesis," 1904, p. 87. 



