Chap. 2.] Micro/copied Appearance of the Blood. 85 



of oxygen, render the above opinion highly pro- 

 bable. 



The fibrous part of the blood, when thoroughly 

 warned, is white and infipid ; by diftillation, like other 

 animal matters, it affords water, oil and volatile alkali. 

 Expofed to a gentle heat, it is much hardened ; when 

 fuddenly expofed to a ftrong heat, it Iririnks up like 

 parchment. It putrefies very rapidly, and affords 

 much volatile alkali. It is infoluble in water, and when 

 boiled in that fluid hardens, and afiumes a grey colour. 

 Acids unite with it, and in particular the nitrous acid 

 difiblves it, and extricates azote and nitrous air; while 

 the refidue by evaporation affords acid of fugar in cryf- 

 tals, a peculiar oil in flocks, and the phofphoric fait of 

 lime. Marine acid forms a green jelly with the 

 fibrous part of the blood. The acid of vinegar diffolves, 

 it with the affiftance of heat ; water, and more parti- 

 cularly alkalis, precipitate the fibrous matter when dif- 

 folved in acids. The animal fubftance is decompofed 

 in thefe combinations ; and when feparated from the 

 acids by any method, it no longer retains its former 

 properties. 



The microfcopical appearances of the blood have 

 attracted great attention. Various accounts have been 

 publimed on this fubjeft, mod of which feem to have 

 been framed more on theory and pre-conceived opi- 

 nion, than actual obfervation. Thefe falfities have 

 been detected by Mr. Hewfon, whofe microfcopical 

 experiments on the blood are the lateft which have been 

 made, and remain at prefent (as far as relates to the 

 compofition of the blood) uncontradicted. I ihall 

 therefore tranfcribe the following particular account of 

 them, given by himfelf in a letter to Dr. Haygarth, 

 phyfician, in C heller. 



G 3 



