166 Scientific Proceedings, Royal Dublin Society. 



first be infected with a very few germs, and then poured into the 

 vessel, which is at first merely plugged with sterilised cotton-wool, 

 and, when suitable development has taken place, is sealed. The 

 appearances thus brought to view are those peculiar to the organism 

 in what is called plate cultivation, and if the glass wall of the 

 vessel be of a certain thinness, it is possible to make out very 

 characteristic details under a low microscopic power. But even to 

 the naked eye the colonies present peculiarities which are easily 

 seized and often quite distinctive. We have here, for instance, the 

 peculiar outlying streamers of this CladotJirix species : the ringed 

 and mouldy looking colony formed from the Ringworm-fungus, 

 Trichophyton tonsurans, and the pellucid dots of Actinomyces 

 with the characteristic yellowish, opaque, stellately arranged mass 

 already making its appearance in the middle of some of the most 

 advanced. The Tubercle bacillus forms extremely characteristic 

 colonies on agar-agar ; but unfortunately I have not a specimen 

 to show you here to-night. 



We now turn to the museum-cultures on potato and turnip 

 or beetroot. Here the difficulties in the course of preparation 

 are very slight, indeed ; anyone accustomed to bacteriologal 

 manipulation can obtain magnificent cultures of most organisms 

 on these vegetable substrata, and enclose them free from contami- 

 nation in vessels suitable for museum purposes. Here is a series 

 on slices of potato which have been placed in small glass pots, 

 sterilised and inoculated, and the lids fastened down with liquid 

 paraffin. And here is a remarkable collection of cultures on red 

 turnip, which show an extremely luxuriant and in many cases 

 characteristic development. The various species of Saccharomyces 

 and the pathogenic hyphomycetes and moulds grew splendidly on 

 potatoes and turnips ; witness amongst others the preparations of 

 S. albus, S. glutinis, Achorion Schdnkinii, Trichophyton tonsurans, 

 Aspergillus niger, A. fumigatus. But it is the chromogenic 

 bacteria which form specially beautiful museum specimens on 

 these opaque substrata, particularly on potato, which, when pro- 

 perly manipulated, may be made to offer an almost pure white 

 background. I need only allude to the bright red layer of J3. 

 prodlgiosus, the brick-red of B. indicus ruber, the brownish-red of 

 a well-known water bacillus, and the violet of another species 

 from the same source ; the peculiar greenish discolouration caused 



