148 



SCIENCE-GOSSIP 



I_JULY J, 1SG5. 



DIATOMS FROM GUANO. 



ri'UIE excellent article on " Cleaning Diatomacese" 

 -^ in the number of Science Gossip for 

 March leaves but little to be desired on that point. 

 Yet, notwithstanding all the care that may be taken, 

 many operators, especially those on guano, will feel 

 dissatisfied with the results they obtain, on account 

 of the mass of foreign matters which, with all their 

 care, will still cling to their deposits, and mar tlie 

 beauty of their slides. To those who may be 

 desirous to obtain fair preparations without this 

 defect, I would recommend a modification of a plan 

 hinted at by Carpenter, and which I have practised 

 with some success. 



I take a slide, well cleaned, and with a dipping- 

 tube put a narrow line of the deposit along its 

 margin : the line should not be more than one inch 

 long, and a quarter of an inch broad. I then place 

 the slide under a simple microscope of moderate 

 power, and I can easily distinguish the different 

 diatoms, even those that are small. I select a large 

 one at first, and with a stout needle I push it out of 

 the water, a thin stream following towards the 

 centre of the slide. When near the centre, I raise up 

 gently the remote edge of the slide, and then push 

 the diatom out a little, when it becomes " high and 

 di-y" on the centre of the slide. In a similar 

 manner, one after another, I put out as many as I 

 please to select, the process becoming easier as I 

 proceed, as the water returns more readily with the 

 needle, and leaves the diatom dry in its proper place. 

 Having exhausted the store of select diatoms in the 

 line, I wipe it off carefully without touching the dry 

 diatoms, and then I put down with the dipping-tube 

 another similar narrow Kne, and proceed as before. 

 I have, in this way, on one slide, taken the choice 

 diatoms out of twenty such narrow lines. No doubt 

 it reciuired time and skilful manipulation, but it 

 became very pleasant and interesting, every fresh 

 portion of deposit laid down affording fresh objects 

 for search, and sometimes new prizes for preserva- 

 tion. The number of diatoms which I place on one 

 slide varies according to the circumstances. On 

 one occasion the first search gave me a specimen of 

 AuUscus formosus : this I put out and mounted 

 alone, a perfect disc, and a beautiful object, which 

 of itself repays me for the time occupied. At ano- 

 ther time, after putting out a number, I obtained a 

 valve with eight highly inflated marginal processes, 

 an example of which I have not yet seen figured. I 

 was then satisfied, and mounted the slide ; but in 

 ■general I proceed until I have nearly two hundred 

 perfect and clean discs nicely placed in the centre of 

 a slide ; and in no case have I occupied more than 

 one long evening of a summer day in the prepara- 

 tion and mounting of one of my slides. 



When a sufficient number of diatoms have been ob- 



tained, they appear to the naked eye as a small cir- 

 cular white spot on the slide. I then heat the slide 

 on a brass table, and take some balsam on a stout 

 w"ire, and place a thin circle of the balsam round the 

 diatoms, taking care to place just so much as maybe 

 required. I then drop a circular cover on the 

 balsam, which speedily runs in and fills the space 

 under the cover without disturbing the diatoms. I 

 then place the slide in a drawer, lying flat for a week 

 or two, until the balsam becomes tolerably hard. 



The advantages of the above method will be, in 

 part, apparent from what I have said ; I may, 

 therefore, only mention, that by it the student 

 would become quite familiar with the appearances of 

 diatoms in w^ater, dry, and in balsam ; and it is 

 needless to say that these appearances vary, and are 

 instructive. Further, slides can thus be obtained, 

 each containing only one sort of diatom, and this will 

 be often desirable for scientific purposes. 



Before closing this paper, I wish to mention a few 

 of the results of my observation in working Peruvian 

 guano by the method I have given. Auliscus 

 Peruviamcs, which has been figured in the Micro- 

 scopical Journal, is a diatom rather small ; in water 

 it appears of an even tawny or yellow colour, deli- 

 cate, and not very attractive in appearance. When 

 dry it becomes quite opaque, and the two processes 

 of a single valve shine brightly in the gloom of the 

 general appearance. 



In balsam it becomes very transparent, and re- 

 quires a tolerably good glass and proper illumination 

 to display the faint markings of the now interesting 

 valve. Another diatom of the class Auliscus appears 

 in water reddish and delicate — dry it seems dark and 

 lurid— and in balsam grey, with sometimes a reddish 

 centre when seen mider a low power. Nothing 

 could be more different than the appearances of 

 these diatoms in the three different mediums. 



Again, a small diatom of the class Astero- 

 lampra, when put out of water with a needle, dries 

 quickl}', becomes quite dark in colour, and then 

 jumps like a flea, an inch or two to one side, or it 

 may be off the slide altogether. Should it be on the 

 slide, it can easily be pushed back dry to the others ; 

 but if the needle be so damp as to wet the diatom, 

 it quickly dries, and then jumps again. Diatoms 

 of this class are, for the most part, most distinctly 

 marked when dry. 



Many other things worth note might be added, 

 but enough has been said for the present. In giving 

 the above, I do not mean to advocate the ex- 

 clusive adoption of my plan. It is well that 

 various methods should be in use, as each may lead 

 to the discovery of facts contributing to the mass of 

 general knowledge. Besides, many may be deficient 

 in patience and manipulative skill for success in its 

 adoption ; but I feel persuaded that many more 

 who fail in cleaning their gatherings and mounting 



