Report on the Bacteriology of Water. 277 



Fourth, the slip with its hanging drop is now cemented as a roof 

 to the cell by running melted sterile gelatine between it and the 

 latter. 



A little practice enables one to prepare such a culture in a few 

 minutes, and very rarely need one go wrong if care is taken. The 

 chief difficulties are with fluid drops, or very dilute gelatine, since 

 they are apt to spread and run over the glass, especially when the 

 air is moist and condenses quickly on the glass surface ; in these 

 cases, however, a little experience enables one to avoid letting the 

 cover-slip get too cold before the drop is attached though, of 

 course the opposite danger has to be guarded against. 



Having isolated a single spore, suspended in the drop of nutrient 

 medium beneath the objective the observations were made with 

 Swift's l/20th and Zeiss' l/12th oil immersion, and with Zeiss' E, 

 occ. 4 a drawing of the freshly sown spore was at once made. The 

 culture was then left, with a bell- jar, darkened with black-paper over 

 the whole, at a temperature of 15 to 20 C,*. and further observa- 

 tions and drawings made at intervals. Naturally there were many 

 failures, especially with the high-power immersion lens, and the 

 following successful series were only obtained at intervals from 

 cultures in which the thickness of the cover-slip, and of the hanging 

 drop, the sufficient isolation of the spore, and the normal germination 

 and further progress were suitable, and where no sudden changes of 

 temperature interfered to check the growth, dry up the gelatine, or 

 cause inconvenient condensations of moisture in the chamber, the 

 relatively large size of which has again proved advantageous owing 

 to the abundant supply of oxygen it ensures. 



Under the conditions referred to, the spore without materially 

 changing its ovoid shape begins to swell somewhat rapidly, and in 

 from one to two hours has increased its dimensions from about 

 1'5 X 2 ft. to 2 x 2'5/4 or more. As it does this the brilliant oil-drop- 

 like contents become duller and more hyaline like ground glass 

 and the sharply marked, almost black membrane, gradually loses 

 some of the firmness of its contour, until it appears as a thinner 

 limiting membrane. At the same time it becomes surrounded by an 

 almost imperceptible pale halo- like investment which appears to be 

 derived from the deliquescence of its most external layers, probably 

 into a soft, transparent, swollen jelly. (Cf. figs. 9 12.) 



In the course of the next one to two hours or so, the spore appears 

 to be elongating. Close observation shows that this is due to a 

 thinning out of the membrane at one of the ends, and soon after- 

 wards the thinned out wall gives way, and the pale, hyaline, 

 apparently homogeneous protoplasm, enveloped in an exceedingly 



* These temperatures are somewhat low, and later results were got at 25 26 C. 

 and higher. 



