THE BLOOD. 211 



those persons in whom for any reason there should be a suppression 

 of periodically recurring haemorrhages, as in menstruation and bleed- 

 ing from the nose. 



Plethora of water, or liydramia, follows the excessive ingestion 

 of water. The condition is but temporary, however, as an increased 

 diuresis rapidly eliminates the excess of water. 



Function of the Blood. Nourishment is carried to the tissues 

 and waste from them by the blood. The sameness of the blood in 

 chemical composition must always be maintained. During digestion 

 the white corpuscles increase, but they soon return to their original 

 number, the excess of corpuscles being retained in the lymphatic 

 tissues. The tissues themselves keep the composition of the blood 

 constant. If some potassium ferrocyanide is injected by the vein 

 into a dog whose ureters have been previously tied, at the end of 

 three hours there is only a small quantity in the blood, and at the 

 end of twenty-four hours only a trace of it. The ferrocyanide has 

 passed into the tissues. Any" disease of the kidneys at once leads 

 to changes in the molecular composition of the blood. The red 

 corpuscles carry oxygen to the tissues. The plasma conveys the 

 carbonic acid combined with sodium to the lungs. The white 

 corpuscles furnish the fibrin-ferment, lysins and complements. 



MEDICO-LEGAL TESTS OF THE BLOOD. 



To determine that a substance under examination and inspec- 

 tion is blood several tests are employed: 



First. Teichmann's crystals, or hsemin .crystals, are a product 

 of decomposition of the coloring matter of the blood. They may be 

 prepared by the addition to the blood of glacial acetic acid and 

 sodium chloride., A few granules of dried blood with a few granules 

 of salt are pulverized on a glass slide; having covered the powder 

 with a glass circle, a drop of the acid is allowed to flow under, when 

 the slide is heated. Tf the examined substance be blood, the char- 

 acteristic crystals appear. 



Second. THE GUAIACUM TEST. On treating a solution of the 

 coloring matter of the blood with an alcoholic tincture of guaiacum 

 and an ethereal solution of hydrogen peroxide, a deep-blue coloration 

 is produced, due to oxidation of the guaiacum resin. 



Third. THE SPECTROSCOPE TEST, in which characteristic bands 

 appear. 



Fourth. Careful measurements of the blood-corpuscles, their 

 diameter, etc., by means of the microscope and photomicrographs. 



