SHARE IN THE VITAL TRANSFORMATIONS. 171 



body. When introduced into the system, they 

 augment the energy of the vital activity of one or 

 more organs ; they excite morbid phenomena in the 

 healthy body. All of them produce a marked effect 

 in a comparatively small dose, and many are poi- 

 sonous when administered in larger quantity. None 

 of the substances in this class can be said to take a 

 decided share in the nutritive process, or to be em- 

 ployed by the organism in the production of blood ; 

 partly, because their composition is different from 

 that of blood, and, partly, because the proportion in 

 which they must be given, to exert their influence, is 

 as nothing, compared with the mass of the blood. 



These substances, wiien taken into the circula- 

 tion, alter, as is commonly said, the quality of the 

 blood, and in order that they may pass from the 

 stomach into the circulation with their entire effi- 

 cacy, we must assume that their composition is not 

 affected by the organic influence of the stomach. 

 If insoluble when given, they are rendered soluble 

 in that organ, but they are not decomposed ; other- 

 wise, they would be incapable of exerting any influ- 

 ence on the blood. 



76. The blood, in its normal state, possesses two 

 qualities closely related to each other, although we 

 may conceive one of them to be quite independent 

 of the other. 



The blood contains, in the form of the globules, 

 the carriers, as it were, of the oxygen which serves 

 for the production of certain tissues, as well as for 



