Bi' Davy on an Economical Mode of using the Potato. 187 



rocks, we find the limestone pass into saccharoid marble ; and 

 we are much embarrassed by so many proofs of an insensible 

 passage from gneiss into sedimentary rocks, — proofs which, 

 of late years, have made the opinion of the origin of gneiss 

 by metamorphism to be almost universally adopted.'* 



On an Economical Mode of using the Potato \ in a Letter ad- 

 dressed to Professor Jameson. By John Davy, M.D., 

 F.R.S., Inspector-General of Army Hospitals, &c. 



My dear Sir, — The sad accounts which I read in the 

 newspapers, of the diseased state of the potato, and its conse- 

 quent decay in most parts of the country at home, and espe- 

 cially in Ireland and the Highlands, bring to my recollection 

 some trials which I made, before I left England, on this 

 root as an article of food, with a view to economy ; a few of 

 the results of which I now beg leave to communicate through 

 you to the public, with the hope of a chance of usefulness. 



It is known to the chemist that the potato consists prin- 

 cipally of starch, of certain juices, chiefly water, impregnated 

 with a variety of proximate principles, and of a cellular 

 fibrous structure in which the starch and the fluid parts are 

 held. 



In the ordinary method of making potato-starch, a rude 

 analysis is eff'ected ; the greater portion of the starch is se- 

 parated from the cellular fibrous structure, and also from the 

 juices of the root. As the process is commonly conducted 

 on a small scale for domestic purposes, there is much waste ; 

 it is only the starch that is preserved, and not the whole of 

 it, for some of it is retained in the cellular structure : the 

 cellular fibrous part with the juices is either thrown away, 

 or, where a stricter economy is observed, is given to the pigs. 



It is to this part, the cellular fibrous, that I wish to call 

 attention, because I believe it to be not without nutritive 

 power, and deserving of care equally with the fecula, the nutri- 

 tive power of which it may even surpass. I am induced to form 



