71 



another. Canada balsam contracts the spores and is apt to contort them. 

 Glycerine pure and simple simply refuses in course of time to remain in the cell 

 of the slide, and works its way out. Glycerine jelly is nearly as bad, and, in 

 common with gelatine medium, contracts and exjiands with the temperature of 

 the weather, and therefore is unreliable. Thwaite's fluid, like water, may be 

 very .successful for a time, but will be sure to change the colour of the tissues 

 eventually. Cami^hor water, and the other media which have been used in the 

 vain attempt of beautifully balancing themselves, so as to check either the growth 

 or decay of the plant, all fail. Nothing on earth is perfect. We may do our best, 

 a? we try to do, but success, however near, is not assured. If anj'one asks me 

 what media I should now use, and recommend others to use, my answer would be 

 — for any fungi that would bear them (and they are not numerous) employ 

 Canada balsam. First take the greatest possible care to keep the spores in their 

 natural jJace by giving them as small a quantity, not of pure spirits of wine, 

 which scatters them, but benzole, which has a different effect. Let the benzole 

 separate, then mount. When Canada balsam will not suit, as is generally the 

 case, I use gelatine, warming all the materials used. Water I may say is, to the 

 best of my knowledge, indispensable when you want to see such portions of a 

 fungus as the zoospores. Much advantage may be gained by putting on the label 

 of the slide not only the name of the object, but the medium in which the same is 

 mounted. I have slides in my cabinet of great scarcity, which it would be next 

 to impossible to replace. Some of them have lost the whole of the medium in 

 which they were placed through evaporation, and are almost valueless. Others 

 have not gone so badly, but there are large bubbles of air in them, which are the 

 forerunners of total evaporation. Had the original mounter of the same named 

 the fluid in which they were placed on the slide there would have been little 

 diflBculty in bringing them back to their primitive condition. 



May I use words of caution to beginners ? Be very careful not to use high 

 power object glasses with high eye pieces -if you want high powers always use 

 low eye pieces. The strain on the eye is not anything like so great when this 

 plan is adopted. Besides, with high power object glasses you may get any 

 amount of magnifying iwwer that is necessary. Again, use as little light as you 

 well can from the mirror. It is a very wrong notion, indeed, that a great light is 

 essential. Always get a subdued light, one that is not in the least liable to strain 

 the eye at all. The definition of the slide wdl be just as good ; mdeed, better— 

 the time occupied will be much better employed, because you will work longer, 

 and the comfort to yourself at work will be considerably improved. Then, again, 

 banish to the winds the idea that you cannot keep both eyes open when working 

 with a single-tubed microscope — monocular as it is called. There are several 

 ways by which this may be effected : — one is by having a black sheet of paper 

 near to the second eye ; another plan is to put your hand before your eye. Per- 

 severance is all that is needed. One evening is quite enough to make anyone 

 skilful in this respect if he is determined to succeed. He need no more fear 

 seeing things on the table with the second eye than seeing the crown of his head, 

 unless he is in training for drawing objects on the table by means of a camera 



