346 PHILOSOPHY OF ZOOLOGY. 
When the coagulated serum is heated in a silver vessel, 
the surface of the metal is blackened, being converted into 
sulphuret. This is the proof brought forward, that the 
serum contains sulphur; but the previous demonstration of 
the existence of albumen rendered it unnecessary, since 
into that substance sulphur appears to enter as an ingre- 
dient of its constitution. 
Clot.—The clot, or crassamentum, as we have already 
stated, consists of the coloured particles which were sus- 
pended in the serum, and with which a portion is still me- 
chanically mixed. If upon the clot, (in a great measure 
freed from the serum, by cutting it into thin slices, and 
pressing it upon blotting paper,) cold water be poured, the 
colouring matter is removed, and the portion which re- 
mains exhibits the properties of fibrin. 
The colouring matter is not dissolved by the water, but 
merely mechanically suspended, and gradually subsides 
when allowed to rest. When thus mechanically diffused, 
the colouring matter coagulates by heat, and may readily 
be obtained upon a filter. This matter appears to be a 
substance intermediate between fibrin and coagulated albu- 
men, but distinguishable from both, by the colour which it 
retains, and the salts which it yields by incineration *. 
Lrem_ery, and several of the earlier chemists, discovered 
iron in the blood. SacE and Green considered that it 
existed in combination with phosphoric acid. Fourcroy 

* Berzerivs found that 400 grains of colouring matter, when burnt, 
yielded 5 grains of ashes, composed of 

Oxide of Tron, - - - 50.0 
Sub-phosphate of iron, - - = 7.5 
Phosphate of lime, with a small quantity of magnesia, 6.0 
Pure lime, - - - - 20.0 
Carbonic acid, and loss, - - 16.5 
100.0. 
Annals of Phil. vol. ii. p. 197. 
