234 Dk. BUCIIAN.VN on tlie White or Opcujue Serum of the JJlooif. 



I conclude with a few remarks upon the physical and chemical char- 

 acters of this variety of serum. 



The colour of the serum is generally a milk-white ; sometimes a 

 cream-yellow ; or a yellowish-brown, when the liquid bears a striking 

 resemblance to thin oat-meal gruel. There is sometimes little dis- 

 colouration, the serum merely losing its limpidity, and changing its 

 hue so as to resemble a weak syrup made of coarse sugar. 



In all the instances in which I have examined the liquid with the 

 microscope, it showed a great number of solid granules mechanically 

 suspended in it. They are less in size than the corpuscles of the 

 blood, generally of irregular shape ; but often spherical, and having 

 the appearance of a nucleus in the centre, most probably from the 

 refraction of light. These particles were as abundant in the syrup- 

 like serum, as in the more opaque varieties; but they were less regular 

 in shape, and seemed to be themselves translucent. 



It sometimes happens, as has been observed both by Hewson and 

 Hunter, that after the liquid has stood for some time, the white particles 

 separate from it, and rise to the surface like cream. Hewson attempted 

 to effect this separation by churning the serum, but without success. I 

 accidentally hit upon a process by which the object is readily effected. 

 It consists in saturating the liquid with common salt, which so much 

 augments its specific gravity, that the opaque particles becoming rela- 

 tively lighter, rise to the surface, either immediately, or soon after. 

 This process has the further advantage of preserving the liquid. I 

 still possess some of the original specimens obtained in November, 

 1840, on which the observations narrated above were made. One of 

 them is the pure serum obtained before the meal. The other three 

 contain white matter, which in two of them is still swimming in the 

 liquid, nearly as when it first separated. In the third, again, the 

 white matter, after swimming at the top for about two years, became 

 denser, and fell to the bottom, where it has since remained. This 

 precipitation was probably owing to the action of the air ; as I have 

 twice known it happen in a single night, when the air was not excluded 

 by filling the phial completely and then firmly corking it. On ex- 

 amining with the microscope the concrete mass, after creaming, it is 

 found to consist entirely of amorphous granules. It is obvious, indeed, 

 that the white particles undergo a change in their mode of aggrega- 

 tion by the action of the salt, as they are readily separable by the filter 

 after it but not at all before it. 



The white matter separated by the filter is insoluble in water, and 

 is thus easily purified from the salt with which it is mixed on the fil- 

 tering paper, by steeping the latter in water, and then cautiously draw- 

 ing off the water holding the salt in solution. Thus obtained it has 

 the form of a fine white powder, which in two specimens in my posses- 

 sion bears a very close resemblance to wheaten flour. On holding a little 

 of it in the flame of a spirit lamp upon a platinum spatula, it was im- 



