430 Dr. E. Smith on the immediate Source of 



rial for reflection in connexion with this difficult subject. These 

 have an interest aUke to the chemist and the physiologist ; and 

 as so little is really known as to the precise mode in which 

 foods perform their function of nourishing the body, any 

 additional facts may also have an interest to the practising 

 physician. 



I purpose to consider the subject in the three following points 

 of view. The carbon evolved at any particular moment is derived — 

 ]st. From the innnediate transformation of food containing 

 carbon. 



2nd. From the blood, in which it is held free or loosely asso- 

 ciated with a base. 



3rd. From the direct transformation of the vital tissues of the 

 body. 



In the papers above referred to, I have shown that there is a 

 uniform and progressive variation in the quantity of carbonic 

 acid evolved after each meal. There is an increase commen- 

 cing within half an hour after the meal, and attaming its maxi- 

 mum in from two to three hours; and from this point the 

 decline commences, and proceeds until the next meal. This 

 occurs after every meal ; and with a suitable interval between 

 the meals, the whole increase is lost before the next meal; 

 but this is not usually the case after the midday dinner meal. 

 The direct connexion of the meal with the increase, and the in- 

 crease and decrease being in a definite order and occupying a 

 certain period, and being connected with the appetite or desire 

 for food, there is the strongest ci jn-iori reason for attributing 

 the increase in the carbon expired to the sapply of carbon which 

 the meals have afforded, and therefore to refer the source of the 

 carbon to the first head. 



But I shall show that this theory is open to two classes of ob- 

 jections, viz. in not accounting for many facts, and in being op- 

 posed by many others. It does not account for the following 

 facts : — 



1st. In a day of fasting there is no noticeable variation, hour 

 by hour, in the quantity of carbonic acid evolved, but a uniform 

 quantity is expired which is so great as two-thirds of the whole 

 quantity evolved with the ordinary meals. Hence this lai'ge and 

 constant quantity cannot be due to the immediate transforma- 

 tion of food. 



The same objection lies in reference to all that large quantity 

 of carbon which is evolved up to the minimum point observed 

 w^ith food, Niz. that which occurs before the meal, and which is 

 the same as is continued through the day in the absence of 

 food. 



2nd. I have proved that when starch or fat is taken alone. 



