BLOOD. 351 



year 1674 ; showed that they are heavier than serum, and rec- 

 koned their diameter 19 1 of an inch.* 



In the year 1747, Menghini, published a memoir in which he 

 proved the existence of iron in the blood, f especially in the red 

 globules. According to him, when preparations of iron are taken 

 into the stomach, the metal speedily makes its way into the blood, 

 when it may be detected by analysis. 



Nothing or almost nothing was known respecting the saline 

 constituents of the blood till Rouelle published his researches on 

 the subject in the Journal de Medecine, for the year 1773 and 

 1776. He observed, that not only the serum of blood, but also 

 the water of dropsies, is coagulated by heat and acids like the 

 white of an egg. He found that these liquids gave a green co- 

 lour to syrup of violets, and concluded that they contain a fixed 

 alkali. This alkali in human blood is soda ; though he showed 

 by combining it with sulphuric acid and crystallizing that some 

 potash was also present in it. Rouelle found, likewise, some com- 

 mon salt, animal earth,:]: and iron in the ashes of blood. The so- 

 da in blood, according to him, is to the saline contents of that 

 liquid as 16 or 17 to 28 or 29. The animal earth constitutes 

 about a tenth of the whole ashes of blood. The iron, he says, has 

 a yellow colour, and in general is attracted by the magnet. In- 

 deed it was by means of the magnet that Menghini separated it. 

 Rouelle examined likewise the blood of the ox, the horse, the 

 calf, the sheep, the hog, the ass, and the goat, and found in it the 

 same salts as in human blood, though with some difference in 

 the proportions, not only in the different animals, but even in 

 the same species. 



He made some experiments on the serum of blood, from which 

 apparently originated the opinion long entertained, that blood 

 contained gelatin as one of its constituents. He evaporated se- 

 rum of blood to dryness over the vapour bath. It then assumed 

 the appearance of glue, with this difference, that it was less solu- 

 ble.in water, and that it had the property of coagulating at the 

 boiling temperature of water. From these properties he con- 

 cluded' that it possessed at once the nature of gelatin and of al- 

 bumen. 



* Phil. Trans, ix. 23, and xxxii. 341. 



f De ferreorum particulorum sede in sanguine. Commentar. Bononiens., 1747, 

 ii. 475. 



\ Afterwards shown to be phosphate of lime. 



