COAGULATION OF THE BLOOD. 225 



way into the blood, and circulates for a time uncoanged. After- 

 ward it disappears as free fat, and remains partly in the saponified 

 condition. 



The saline ingredients of the plasma are of the same nature with 

 those existing in the globules. The chlorides of sodium and potas- 

 sium, and the phosphates of soda and potassa are the most abundant 

 in both, while the sulphates are present only in minute quantity. 

 The proportions in which the various salts are present are very dif- 

 ferent, according to Lehmann, 1 in the blood-globules and in the 

 plasma. Chloride of potassium is most abundant in the globules, 

 chloride of sodium in the plasma. The phosphates of soda and 

 potassa are more abundant in the globules than in the plasma. On 

 the other hand, the phosphates of lime and magnesia are more 

 abundant in the plasma than in the globules. 



The substances known under the name of extractive matters consist 

 of a mixture of different ingredients, belonging mostly to the class 

 of organic substances, which have not yet been separated in a state 

 of sufficient purity to admit of their being thoroughly examined 

 and distinguished from each other. They do not exist in great 

 abundance, but are undoubtedly of considerable importance in the 

 constitution of the blood. Beside the substances enumerated in the 

 above list, there are still others which occur in small quantity as 

 ingredients of the blood. Among the most important are the alka- 

 line carbonates, which are held in solution in the serum. It has 

 already been mentioned that while the phosphates are most abun- 

 dant in the blood of the carnivora, the carbonates are most abun- 

 dant in that of the herbivora. Thus Lehmann 2 found carbonate of 

 soda in the blood of the ox in the proportion of 1.628 per thousand 

 parts. There are also to be found, in solution in the blood, urea, 

 urate of soda, creatine, creatinine, sugar, &c. ; all of them crystalliza- 

 ble substances derived from the transformation of other ingredients 

 of the blood, or of the tissues through which it circulates. The 

 relative quantity, however, of these substances is very minute, and 

 has not yet been determined with precision. 



COAGULATION OF THE BLOOD. A few moments after the blood 

 has been withdrawn from the vessels, a remarkable phenomenon 

 presents itself, viz., its coagulation or clotting. This process com- 

 mences at nearly the same time throughout the whole mass of the 

 blood. The blood becomes first somewhat diminished in fluidity, 



1 Op. cit., vol. i. p. 546. 2 Op. cit., vol. i. p. 393. 



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