50 HUMAN PHYSIOLOGY. 



case having nothing to do with the change. This view is supported by the 

 fact that the quantity of fibrin obtained from the blood is never greater than 

 the quantity of fibrinogen previously present. The origin of the ferment is 

 obscure, but there is reason to believe that it comes from the injured vascu- 

 lar coats or from the breaking of the white corpuscles. 



Conditions Influencing Coagulation. The process is retarded by 

 cold, retention within living vessels, neutral salts in excess, inflammatory 

 conditions of the system, imperfect aeration, exclusion from air, etc. 



It is hastened by a temperature of 100 F., contact with air, rough sur- 

 faces and rest. 



Blood coagulates in the body after the arrest of the circulation in the 

 course of 12 to 24 hours; local arrest of the circulation, from compression 

 or a ligature, will cause coagulation, thus preventing hemorrhages from 

 wounded vessels. 



The Composition of the Blood varies in different portions of the body. 

 The arterial differs from the venous, in being more coagulable, in contain- 

 ing more oxygen and less carbonic acid, in having a bright scarlet color, 

 from the union of oxygen with haemoglobin ; the purple hue of venous blood 

 results from the deoxidation of the coloring matter. 



The blood of the portal vein differs in constitution, according to different 

 stages of the digestive process; during digestion it is richer in water, 

 albuminous matter and sugar ; occasionally it contains fat ; corpuscles are 

 diminished, and there is an absence of biliary substances. 



The blood of the hepatic vein contains a larger proportion of red and 

 white corpuscles; the sugar is augmented, while albumin, fat and fibrin 

 are diminished. 



Pathological conditions of the blood. 



I. Plethora increase in the volume or quantity of blood. 



3, Anamia deficiency of red globules with increase of water. 



3. Leucocylhemia increase of white and diminution of red corpuscles. 



4. Glycohcemia excess of sugar in the blood. 



5. Urccmia increase in the amount of urea. 



6. Cholestercemia an excess of cholesterine in the blood. 



7. Throjnbosis and embolism clotting of blood in the vessels and 

 dissemination of coagula. 



8. Lipcemia an excess of fat. 



9. Melancemia pigment in the blood. 



