OF FOODS UPON THE EESPIEATION. 
739 
comprehend nearly all the members of the class. This power is not in a definite pro- 
portion to the quantity of nitrogen contained by them, and sugar, which is powerfully 
“ excito-respii-atory,” is destitute of nitrogen. Probably all compound foods containing 
sugar or gluten, or both, are “ excito-respiratory.” The principal ferments are “ excito- 
respiratory.” 
4. Eespiratoiy excitants haTe a temporary action ; but the action of most of them 
commences rery quickly, and attains its maximum within one hour. 
5. The most powerfiT respiratory excitants are tea and sugar ; then coffee, rum, milk, 
cocoa, ales, and chicory ; then casein and gluten, and lastly, gelatin and albumen. The 
amount of action was not in uniform proportion to their quantity. Compound aliments, 
as the cereals containing several of these substances, have an action greater than that of 
any of their elements. 
6. Most respiratory excitants, as tea, coffee, gluten and casein, cause an increase in 
the evolution of carbon greater than the quantity which they supply, whilst others, as 
sugar, supply more than they evolve in this excess, that is, above the basis. No sub- 
stance containing a large amount of carbon evolves more than a small portion of that 
carbon in the temporary action occurring above the basis line, and hence a large portion 
remains unaccounted for by these experiments. 
7. The som-ce of the carbon evolved, whether directly from the food recently taken, 
or indirectly from increased action induced in the tissues, or from the more rapid dis- 
engagement of that contained in the blood, has not been determined; but it has been 
shown in reference to the rapidity and amount of action of foods, 
a. That the increase in the evolution of carbonic acid with some of the respiratory 
excitants is considerable in Eom three to eight minutes after the introduction of the 
substance into the stomach, and increases regularly and quickly to a maximum, and 
then often declines rapicUy, as is well shown by tea and sugar. In others, as casein, the 
action is more tardy. 
/3. That the effect of alcohols upon the sensorium was often perceived in four minutes 
after they had been swaUowed; and the effect of the inhalation of alcohols over the 
chemical and physical changes was immediate. 
y. That alkalies usually lessen and prolong their action. That fat and the absence of 
fluid lessened the action of sugar, whilst acids often increased its action. 
That small quantities, often repeated, were more efficacious than one large dose. 
e. Also that the whole of the carbonic acid evolved under the influence of tea, coffee, 
and gluten, could not have been derived from those substances. 
It is lemarkable that starch and fat, which constitute the chief supply of carbon to 
the s>-stem, scarcely increase the respiratory changes beyond the amount in which they 
are found in the absence of food. This may help in the elucidation of their interme- 
diate transformations. Fat never, and lactic acid seldom, increases the respiration above 
the minimum line. Grape-sugar is a less powerful respiratory excitant than any other 
kind of sugar; but I have not determined its influence when given in the doses in which 
5 E 2 
