50 Dr. Buchanan on the State of the Blood after taking Food. 



after a meal consisting of various articles of food in common use tho 

 serum of tho blood becomes white or otherwise discoloured, and con- 

 tinues in that state for a period, longer or shorter according to cir- 

 cumstances. It could not be determined, from tho observations then 

 narrated, whether this discolouration be produced by every sort of 

 food, or follow only certain kinds of it. The present communication 

 is principally intended to supply that deficiency, by giving an account 

 of the effects of various simple alimentary principles, or definite com- 

 binations of such simple aliments upon the colour of tho blood. 



Another object which I have kept in view is to give an account of 

 a white substance different from that which gives the opaque colour 

 to the serum of the blood, but which closely resembles it in appear- 

 ance, and exists in the serum still more generally and in greater 

 abundance. It first became known to me in the course of these 

 investigations. It exists both in the opaque serum and in that which 

 is transparent, and is precipitated by supersaturating the liquid with 

 common salt, or with sulphate of soda and certain other salts to bo 

 hereafter mentioned. It is characterised by being immediately re- 

 dissolved on adding a little more water than sufficient to re-dissolve 

 the excess of salt, while it is again precipitated by adding the salt to 

 supersaturation. 



I intended, farther, to have discussed the question of the existence 

 in the blood of a fermentable principle, yielding carbonic acid gas on 

 being treated with yeast; and had made a great variety of experi- 

 ments with that object in view: but not having had sufiicient time to 

 repeat those experiments, so as to satisfy myself as to the true inter- 

 pretation of them, I have omitted the subject altogether, except where 

 it is incidentally introduced. 



The investigations were conducted, as formerly, by examining the 

 blood drawn from persons, who, after fasting from sixteen to twenty- 

 four hours, had taken a full meal consisting of some simple aliment, 

 or combination of such aliments. I shall narrate the observations 

 nearly in the order in which they were made ; and, as nearly as pos- 

 sible, in the words in which they were originally recorded ; as there 

 will be less chance of error in this way than if I attempted to arrange 

 and abridge them. I conceive, also, that a detailed account of these 

 observations may not be without use to those who shall hereafter, I 

 hope with better success, engage in similar inquiries : an object which 

 should be kept more especially in view by physiologists, as their 

 observations cannot, like experiments in the physical sciences, be 

 repeated at will, but require opportunities not always to be obtained, 

 and of which, therefore, the most ought to be made. This must also 

 be my excuse for introducing sundry observations on the state of the 

 blood not immediately bearing on the subject of this memoir. 



I begin by giving an account of the effects of Gelatin on the blood, 

 with respect to which two series of observations were made. 



