Du. Buchanan on the State of the Blood after taking Food. 57 



economy to the other ingredients of the blood, as no longer to disturb 

 their chemical equilibrium. 



Reflections not less important are suggested by the fact brought out 

 by both the two last experiments, that the serum of the blood after 

 a fast of sixteen hours gave a precipitate with salt added to supersa- 

 turation. Was the fast not strictly observed by men who might 

 naturally be supposed to care little for the result of the experiment, 

 and more for their breakfast of which they were deprived? Was the 

 white matter from the supper of the previous night? or, lastly, does 

 all serum give a white precipitate with salt? To this last query, which 

 I had both put to myself, and which had been put to mo by others, I 

 had hitherto answered in the negative, relying upon a specimen of 

 beautifully limpid serum which has been in my possession since 1840, 

 and was shown to the Society last spring, and which I believed to 

 havo been saturated with salt, when most probably no more had been 

 dissolved in it than was necessary to keep it from decomposing. Now, 

 however, that the inquiry was again forced upon me, I examined a 

 great many specimens of the serum of blood ; and I found all of them, 

 without exception, to give a precipitate with salt, although in very 

 different degrees of abundance. I next examined the liquid of the 

 serous cavities, thinking that possibly it might not be effused till the 

 secondary digestion was completed. In this, however, I was mistaken, 

 as all the specimens of hydrocelic fluid which I examined gave a white 

 precipitate with salt 



I was thus fully satisfied that in all ordinary circumstances serum 

 contains a white matter precipitable by salt This, however, is by no 

 means inconsistent with the opinion, that the white matter in ques- 

 tion is the nutritious part of the food absorbed from the digestive 

 passages, but, on the contrary, renders that opinion the more probable. 

 Iodine taken so as to saturate the system, is found in the blood, in 

 the liquid of the serous cavities, and in the synovia of the joints ; and it 

 may be detected in the excretions not only as long as the medicine 

 continues to be taken, but for four days thereafter.* If then a sub- 

 stance taken once or twice daily, to the extent of a few grains, con- 

 tinues so long within the body, it is surely not surprising that we 

 should find there as uniformly traces of our food, which we take 

 three or four times a-day or oftener, to the extent of several pounds. 



It was, however, desirablo to determine with greater accurary, 

 whether the white matter precipitated by salt from the serum of the 

 blood was really derived from the recently taken food. To accomplish 

 this object, three methods of proceeding suggested themselves, viz.: — 

 to compare the quantity of precipitable matter found after taking 

 food — 1st, with that found in the serum of a person who had fasted, 

 honafidc, for twenty-four hours — 2d, with that obtained from a person 



* London Med. Gaz., 1836. 



