300 THE MICROSCOPIST. 



to obtain haemin crystals. A portion of the supposed 

 blood-clot is placed on the slide, and a drop of water con- 

 taining a trace of salt is added. A thin glass cover is 

 applied, and a little glacial acetic acid is allowed to flow 

 in and mix with the blood. Heat is applied until the 

 mixture almost boils. The slide is then placed under the 

 microscope, and the rhomboidal crystals may be observed 

 with a J-inch objective. 



For microspectroscope appearances, etc., see page 102. 

 The guaiacum test, as it is called, depends upon the ozone 

 of the hsemaglobulin of the blood causing a bluish tint 

 in the solution of guaiacum. The tincture is made by 

 dissolving one part of the resin in six parts of alcohol of 

 eighty per cent. The bottles are to be only half filled, so 

 that the tincture may be in contact with the air. Strips 

 of white blotting-paper are soaked in this and the alcohol 

 allowed to evaporate. A weak solution of blood dropped 

 on the paper produces a blue color. This is only valuable 

 as a negative test, since other substances give the same 

 reaction. If no color is obtained, blood is not present. 



^ II. EXAMINATION OF URINE. 



Healthy urine contains a variety of organic and inor- 

 ganic substances, as urea, uric acid, alkaline and earthy 

 salts, animal extractive, vesical mucus, and epithelial 

 debris. A drop or two evaporated on a glass slide will 

 show the crystalline matters, consisting of urea, urate of 

 soda, chloride of sodium, phosphates, and sulphates. 



Before examining urine for the purpose of diagnosis, it 

 is necessary to be familiar with the appearance of the 

 contents of healthy urine, as \vell as of accidental sub- 

 stances which are likely to be met with, as fragments of 

 hair, wool, feathers, cotton, silk, and flax, particles of 

 starch, breadcrumbs, sand, vegetable fibres, etc. Igno- 



