NUTRITION. 299 



4. No one can doubt that the system is continually un- 

 dergoing changes. vThis is proved by the losses to which it 

 is subjected ; by the necessity of frequent supplies of ali- 

 ment ; by the rapid wasting of flesh on the withdrawal of 

 food ; and by the emaciation caused by sickness and old age. 

 It is also shewn by an experiment, which has often been 

 made, viz. of giving madder to animals mixed with their 

 food ; which in a short time tinges their bones of a red 

 colour. If the madder be withdrawn, the red colour in a few 

 days disappears from the bones ; evidently from the effects 

 of absorption^ 



5. Every part of the body is subject to this constant 

 change of matter. While one set of vessels, the lympha- 

 tics, are taking to pieces and carrying away the various 

 oarts of which the machine is composed, another set, viz., 

 |He capillaries, are constantly at work, repairing the loss,] 

 depositing bone, muscle, cartilage, nerve, tendon, fat, mem. 

 brane, ligament, hair, nails, <Szc. where each is wanted, and 

 this with such regularity and order, as to preserve the shape, 

 size, and appearance of every organ, so that, though after an 

 interval of a few years there may not remain in the body a 

 single particle of which, at the former period, it was made 

 up ; still, the individual preserves the same form and features ; 

 his personal identity is never lost. 



6. [Those animals, which are the most complicated in 

 their structure, and are distinguished by the greatest variety 

 of vital manifestationsjare subject to the most rapid changes 

 of matter. Such animals require more frequent, and more 

 abundant supplies of food, and in proportion as they are ex- 

 posed to a greater number of external impressions, so will 

 be the rapidity in this change of matter. The frog, for in- 

 stance, has been dug from the earth many feet below its sur- 

 face ; and even taken from cavities in solid limestone, where 

 he had been shut up probably for centuries, and still exhibit- 

 ed signs of life when exposed to the open air. As he was so 

 situated as to lose nothing, by secretion or evaporation, of 



