8Q PHOTO-MICROGRAPHY 



spoil the tube. It is necessary, therefore, to have quite close at hand some cold 

 water to instantly add to the bath, for the slightest delay has, in our hands, on one 

 or two occasions produced the very disaster we wished to avoid. 



Another hint to remember is to cleanly wipe out the water-bath each time after 

 using, for if water be left in it when not in use it will slowly evaporate and leave 

 ridges of stain on the inside faces of the glass, which have in our own experience 

 given rise to considerable trouble to remove. ( We have found that spirits of wine 

 or very dilute hydrofluoric acid, about 20 drops to the ounce, the best for this 

 purpose.) 



A difficulty arises sometimes when photographing the obliquely filled streaked 

 culture tubes from condensation within the tube itself This constitutes a most formid- 

 able trouble, and one which on some occasions we have been unable to avoid. If leave 

 be granted to move the paraffin wax and woollen plug — to do which gently insert a 

 slightly warmed penknife around the wax at its contact with the glass — the best 

 plan for getting rid of this annoying trouble is to take a stifl* roll of blotting paper 

 of the thin filter-paper type, and very gently insert it down the tube. One touch of 

 the culture may spoil it hopelessly, so the treatment requires the greatest of care, 

 and, as before stated, should never be done without the leave of the bacteriologist. 

 It should be recollected, too, that, if the growth be touched, the paper should 

 be at once immediately burned and the wool and wax returned to their place, 

 recollecting to put the wool in first, and then the melted wax seals up the tube. 



Examples are given of this kind of photography in Plate Y., which are by 

 the kind permission of the publishers taken from the " Atlas of Bacteriology," of 

 which the writer is joint author. 



Enlarging from the Primary Negative. — Occasionally an original negative 

 may have been taken too small to satisfy the requirements of its owner, and so 

 requires enlargement — a remark that applies to photo-micrography in all its branches ; 

 hence we think it advisable before proceeding further to explain how this can be done 

 very easily if only a few copies are required. 



For example, let it be supposed that a low-power negative of a spider has 

 been taken to fill a lantern-plate and it is required to enlarge it from the negative so 

 as to fill a page of this book. The arrangement is shown on page 29 (Fig. 18), 

 where it is seen the large condenser and limelight are again used, but the camera 

 is reversed in position. 



The light will now pass through the negative first (the plane side being turned 



