Dr. Buchanan on the State of the Blood after taking Food. 59 



permit, to deprive the blood altogether of its white precipitate. This 

 conclusion is quite conformable to what our experience of the persist- 

 ance of Iodine in the body would lead us to expect It has, however, 

 been ascertained that the white precipitate obtained from the serum 

 of the blood by suporsaturation with salt, is most abundant after a 

 meal ; that it is less abundant as the period of taking food has been 

 more remote ; and that, after a fast of twenty-four hours, it is very 

 insignificant in quantity. Still farther, after certain kinds of food, 

 such as eggs, casein, and white-fish, a much larger quantity of white 

 matter is found in the serum than after certain other kinds of food, 

 such as starch. Last of all, the characters of the precipitate vary, so 

 that it may either be made to swim on the surface, or sink to the 

 bottom, according to the kind of food. It appears, therefore, not 

 unreasonable to conclude, that this white precipitate proceeds from the 

 food, being tho newly digested nutritious matter introduced by certain 

 aliments into tho blood. 



The only other view that can be taken of tho nature of this preci- 

 pitate, is, that it is occasioned by the salt re-acting upon the albumen 

 dissolved in the serous liquid. This view does not seem to me recon- 

 cileable with the great variations in the quantity of tho precipitate, 

 without any corresponding difference in the quantity of the albumen. 

 Thus in a specimen of hydrocelic serum, of which the specific gravity 

 was 1*038,* the precipitato was so scanty as merely to render the liquid 

 a little turbid ; and in another specimen of the same kind of serum, of 

 which the specific gravity was only 1*025, the precipitate was in great 

 abundance. The following considerations and experiments may serve 

 to elucidate this question. 



After finding that hydrocelic serum gave a precipitate with salt, I took the 

 opportunity afforded by my getting a plentiful supply of that liquid, to resume the 

 inquiry mentioned above, as to whether any other saline substances acted in the 

 same way upon serum as common salt. I first tried the sulphate of soda, which I 

 found to produce the same effect as the common salt, only I thought the precipitate 

 for the most part more abundant. I found also that this precipitate was immedi- 

 ately rcdissolved on the addition of water, and was again thrown down on super- 

 saturating with the sulphate. On afterwards trying this salt with the serum of the 

 blood, I found that the precipitate obtained sometimes floated, and sometimes fell 

 to the bottom, and that in this respect there was not always a correspondence in 

 the action of the two salts on the same liquid. 



I found sulphate of magnesia to act in the very same way, so that I have since 

 been in the habit of employing commonly these three salts as prccipitants. 



I found that neither the sulphate of soda nor the common salt threw down the 

 whole precipitable matter contained in the serum. To show this, I saturated some 

 scrum with each of these salts separately. I then removed the precipitates by the 



* This specific gravity is, I believe, the highest upon record of any serous liquid. The 

 serum was taken from one of the strongest men in this city, who has laboured under 

 hydrocele for about ten years, and from whom I have regularly removed it at intervals 

 of from six to ten months. The specific gravity mentioned above was determined by the 

 hydrometer, but to remove all doubt, I had it again determined with great accuracy by 

 the balance, when it was found to be 1*0377. 



