32 HOW TO PHOTOGRAPH MICROSCOPIC OBJECTS. 



Brucia must be crystallized from alcohol. 

 The crystals are oblique rhombic prisms. 

 It dissolves in balsam rather rapidly, so 

 should be either set up dry or in castor oil. 



Atropine, caiTeine, and narcotine crystal- 

 lize in needles. The former must be mount- 

 ed dry. Morphia, and morphia chloride, 

 sulphate, and acetate may be crjstallized 

 either from water or alcohol, and mounted 

 in balsam. 



Quinfne sulphate gives a profusion of 

 silky needles from a dilute alcoholic so- 

 lution. Owing to their delicacy they are 

 difficult to preserve, but may be mounted in 

 dilute balsam and benzole. 



Sulphur must be dissolved in carbon bi- 

 sulphide. The best crystals are obtained 

 in winter; but at all times of the year the 

 solution must be evaporated in a room quite 

 free from draughts, and as cool as possible. 

 These crystals must be photographed by re- 

 flected light with a low power. Salicine is a 

 very favorite microscopic object ; but the 

 splendid discs usually seen on slides are only 

 modifications of the typical acicular crystals. 

 The real forms are best obtained from a 

 dilute aqueous solution, which may be hot. 

 If a little gelatine be added to the solution, 

 delicate discs form on crystallization, which 

 are seen to consist of needles radiating from 

 a common centre. Fusion of the dry salt 

 gives only coarse discs, but if a concentrated 



aqueous solution be made, and evaporated 

 over a lamp until fusion just commences 

 very delicate discs of a larger size may be 

 obtained. One method of obtaining fine 

 discs is to put a solution of salicine in gela- 

 tine on a glass slip. Warm the slip over the 

 lamp for a few moments, and then pour the 

 solution off ; enough will be left on the 

 slide to form a thin fikn. The film is then 

 pricked in several places with a fine needle, 

 and immediately crystallization commences, 

 from each prick as a centre, and goes on all 

 over the slide. The whole is at once cover 

 ed with balsam and benzole, and a thin glass 

 square gently pressed on. If not covei-ed at 

 once, the crystals become opaque. 



Santonine and phloridzine are crystallized 

 from an alcoholic solution, and may be pre- 

 served in balsam. 



Here our Lessons in "Photo-microgra- 

 phy" are brought to a close. The student 

 must once more be reminded that skill in 

 manipulation of the microscope will not by 

 itself produce the best results. There must 

 be not only expertness in each photographic 

 operation, but an intelligent understanding 

 of the why of each process. Photography 

 as a science must be studied by itself, and 

 for itself ; for it is only when an intelligent 

 understanding, both of microscopy and pho- 

 tography, is gained, that photo-micrography 

 becomes worth pursuing. 



