336 PLEASANT WAYS IN SCIENCE. 



by a continual and sufficient supply of fibrine and albumen, 

 the result will be a gradual lowering of all the powers of the 

 system, until some one or other gives way, the heart ceases 

 to beat, or the stomach to digest, or the liver to secrete bile, 

 and so death ensues. 



The fibrine and albumen in the animal frame are derived 

 exclusively from vegetables. For although we seem to 

 derive a portion of the supply from animal food, yet the 

 fibrine and albumen thus supplied have been derived in the 

 beginning from the vegetable kingdom. " It is the peculiar 

 property of the plant," says Dr. Lankester, "to be able, in 

 the minute cells of which it is composed, to convert the car- 

 bonic acid and ammonia which it gets from the atmosphere 

 into fibrine and albumen, and by easy chemical processes 

 we can separate these substances from our vegetable food. 

 Wheat, barley, oats, rye, rice, all contain fibrine, and some 

 of them also albumen. Potatoes, cabbage, and asparagus 

 contain albumen. It is a well-ascertained fact that those 

 substances which contain most of these ' nutritious secre- 

 tions,' as they have been called, support life the longest." 

 They change little during the process of digestion, entering 

 the blood in a pure state, and being directly employed to 

 renew the nervous and muscular matter which has been 

 used up during work, either mental or muscular. Thus the 

 supply of these substances is continually being drawn upon. 

 The carbon, which forms their principal constituent, is con- 

 verted into carbonic acid ; and the nitrogen, which forms 

 about a sixth part of their substance, re-appeais in the nitro 

 gen of urea, a substance which forms the principal solid 

 constituent of the matter daily thrown from the system 

 through the action of the kidneys. Thus the amount of 

 urea which daily passes from the body affords a measure of 

 the work done during the day. "This is not," says Dr. 

 Lankester, " the mere dream of the theorist ; it has been 

 practically demonstrated that increased stress upon the 

 nervous system, viz., brain work, emotion, or excitement 

 from disease, increases the quantity of urea and the demand 



