BLOOD. 



I// 



1, Those errors against whicli we may guard by caution ; and 



2, Those which, with all care, cannot be avoided. 



Water. This constituent may be determined with perfect 

 exactness. 



Fibrin. If the blood be whipt with due care, the fibrin is 

 obtained as a thick, coriaceous, fibrous mass, surrounding the 

 twigs of the rod. It can be removed without loss, and can be 

 easily and quickly washed. 



If it be stirred too rapidly, a portion of the fibrin becomes 

 minutely subdivided, and after washing cannot be collected 

 without some loss ; on the contrary, if it be stirred too slowly, 

 or not long enough, the fibrin incloses many blood-corpuscles, 

 and must either lie for some time in water, during which it is 

 liable to a certain degree of change, or else it must be tri- 

 turated and broken up, which induces the formation of flocks 

 and of a viscid matter, and occasions considerable loss. 



With a little experience and practice, the fibrin may be de- 

 termined with great exactness. It is necessary to submit the 

 dried fibrin to a temperatui'e of 230°. 



Fat. The fat contained in the fibrin may be estimated 

 with great accuracy. It is only necessarj'- to boil the pulverized 

 fibrin with ether, or (which is better) with a mixture of ether 

 and anhydrous alcohol, for four, five, or six times. The deter- 

 mination of the quantity of fat in the dried pulverized blood is 

 much less certain and accurate. In an analysis in which I 

 separated the hsemaphsein, I treated a large quantity of pul- 

 verized blood, six successive times with boiling ether, in a 

 retort ; yet I still found a considerable quantity of fat in the 

 hsematin. Tliis may be due, partly to the compounds of mar- 

 garic and oleic acids becoming decomposed by the sulphuric 

 acid in the alcohol dm-ing the boiling of the powdered blood 

 which had been treated with ether ; and partly, I believe, to a 

 little free fat which had not been taken up by the ether. 



The fat appears to be extracted most perfectly when the 

 powdered blood has been first loosened, as it were, with an- 

 hydrous alcohol. A quantity of ether, just sufficient to pre- 

 cipitate the salts dissolved by the alcohol, must then be added. 



12 



