238 



THE BLOOD. 



the particles were annular in form. Most of the recent mi- 

 croscopical observers have satisfied themselves of the correct- 

 ness of Hewson's opinion, that the dark spot in the centre, is 

 owing to the presence of a solid nucleus in each particle. The 

 outer vesicle, which encloses the nucleus, is seen torn, (see 

 fig. 176,) showing the nucleus in one of the red particles of the 

 frog. 



These vesicles contain the coloring matter of the blood, 

 and under particular treatment, are rendered soluble, and the 

 naked nuclei are precipitated in the form of minute granules. 

 Under any treatment, the latter are found to be insoluble. 



Chyle Globules. 



In the blood, Hewson also observed some minute globules, 

 which he considered those of the chyle. They have since 

 been observed by Miiller and others. They are abundant in 

 the chyle, in the lymph, and are probably, as Hewson sug- 

 gested, identical with the nuclei of the red particles. Accor- 

 ding to Prevost and Dumas, their diameter is precisely the 

 same as that of the primitive muscular fibre, the ^ S5 th part of 

 an inch. - 



The color of the blood has, for a long time, been supposed 

 to depend upon iron. About the middle of the last century, 

 Vicentius Menghini published in the Transactions of the Aca- 

 demy of Sciences of Bologna, an account of experiments which 

 contributed to establish this sentiment. In this account he 

 stated that, after washing the coloring matter from the cras- 

 samentum, he had separated it from the water by boiling ; in 

 which case it either rose to the surface of the water, or sub- 

 sided, and left the water clear. After drying with a gentle 

 heat, some of the coloring matter thus separated, and then 

 repeatedly washing it, he found that it contained a consider- 

 able quantity of iron, which was attracted by the magnet. 



After exposing a large quantity of the coloring matter to an 

 intense heat, he found it in a small piece of iron, of a spherical 

 form, but hollow; and a powder which was attracted by the 

 magnet, but appeared more like rust of iron than iron filings. 



