223 Letter to Governor PornwU 



hard and covered with tough skin& ; and therefore l>efore 

 this food can he dissolved and turned into chyle, it must be 

 softened and its skins ground off; the fir^t of which is done 

 by warmtli and moisture in the criw, and the second by 

 attrition in the gizzards By these contrivances the food 

 of fowls is prepared and fitted for digestion, as hinnaii 

 food is by eooker\- and other wavs of preparing it, and 

 by the grinding of the teeth. But if wc should grant thaf, 

 the food of fowls is dissolved and turned into chyle by attri- 

 tion, it will by no means follow that food is so dissolved 

 and turned into chyle in a human stomach, which has no 

 gravel in it, and I'tas but vcrv little muscular strength in 

 comparison of the gizzards of fowls. There may be many 

 different contrivances in different species of animals, to 

 soften, grossly divide, and prepare their food for digestion ; 

 but it will not from thence follow that their food is digested 

 or turned into chyle by differnit causes. 



*' The food is dissolved and turned into chvle bv a gentle 

 heat and motion. Heat makes many bodies fluid which 

 arc not fluid in cold. Lead is melted by a heat eight times 

 as great as the external heat of a human bod)' ; tin, by a 

 heat six times as great ;■ wax, bv a heait twice as great ; and 

 bones, with the addition of a little water, are dissolved in a 

 digester by heat in a little time. If the heat of the stomach 

 be nearly cq-ual to that of the blood, it may be sufficient, 

 Avheu the orifices of the stomach are prcttv exactly closed, 

 to dissolve the food in a few hours, and turn it into chyle ; 

 especially when it is assisted by the motion of the stomach, 

 ■which bv agitating and mixins; the food will contribute to 

 this end. For, since heat can dissolve solid Tx)dies, and no- 

 thing is found in a human stomach, besides a gentle heat 

 and motion, which can dissolve the food and turn it into 

 chvle, it will follow that the food is digested or dissolved^ 

 and turned into chyle, by a gentle heat and motion. 



" The chvle in moving through the intestines is- further 

 dissolved by heat and motion; and the finest part of this 

 fluid being conveyed into the blood, is still further changed 

 by the same' causes, namely, a gentle heat and motion, till 

 Jt puts nn the form of blood, and, at last, becomes fit to 

 nourish ihe body by being made like its solid and durable 

 parts. The growtli of the chicken in the shell out of the 

 white of the egc; is a strong proof of the truth of this : for 

 here is mauifcstlv nothing, besides a gentle heat and mo- 

 tion, to change the white of the eog so as to convert it into 

 blood, and render it fit nourishment for all the parts of an 

 animal bodv. 



" Cor, Hence animals will not be rightly liourished when 



the 



