266 M. C. COOKE ON BLACK MOULDS. 



mode of attachment. Moulds are so microscopical in their details 

 that a less power than 320 diameters will hardly give a satisfactory 

 result. I have tried several methods to ohtain readily, as an 

 opaque ohject, a good view of a small fragment of mould by a 

 one-third or one-fourth objective. By having an objective con- 

 structed, specially for the purpose, with the metal reduced to a 

 minimum, so that the point should be as small and obstruct light as 

 little as possible, I hoped to have been able to direct sufficient light 

 upon the mould to view it as an opacpie object, at least with suffi- 

 cient distinctness to recognise the great features of growing habit ; 

 but all these efforts have resulted in a practical failure, and I have 

 been compelled to revert to the old imperfect method. 



Having satisfied myself with the preliminary observation, a little 

 spirits of wine is placed at the edge of the covering glass, and 

 allowed to enter by capillary attraction, and invest the whole of the 

 mould. Of course the spores will at once all leave their attach- 

 ment, but with the knowledge obtained at the preliminary examina- 

 tion, it will not be difficult now to determine both the genus and 

 species of the mould under examination. For what reason use 

 spirits of wine ? it may be asked. The answer is that unless 

 alcohol, or benzine, or ether, are employed, small bubbles of air will 

 cling persistently about the mould, and no effort will remove them. 

 The threads appear to resist pertinaciously water and glycerine, and 

 determine to float upon them. Thus far, then, we are enabled to 

 examine a mould ; but it may be thought advisable, imperfect as 

 such an object must be when immersed in any fluid, from the 

 speedy displacement of the spores, to have it permanently mounted 

 for future reference and comparison. Such a mounted object will 

 always show the character of the threads, and the size and septa- 

 tion of the spores, and being already mounted to hand, a new mould 

 may at once be compared, whilst under examination, with the spores 

 and threads of twenty or fifty other species, within a few minutes ; 

 whereas, if every one had to be examined anew, a great waste of time 

 and labour, to say nothing of reducing the specimens by a recur- 

 rence of examinations, would take place. I can, therefore, strongly 

 recommend permanent mountings as tests, or types, for comparison, 

 and I count my own collection of such objects by thousands. They 

 are not attractive, perhaps, not always pretty, not well displayed, not 

 available for a public soiree or a private tea party, but they are 

 practically invaluable for scientific work, and by their aid a most 



