THE ACTIONS OF FOECES ON OEGANIC MATTER. 41 



that some of the leading transformations occurring in the 

 animal organism, are due to this so-called catalysis, appears 

 necessitated by the general aspect of the facts ; apart from 

 any such detailed interpretations as the foregoing. We know 

 that various amylaceous and saccharine matters taken as food, 

 are decomposed in their course through the body. We know 

 that these matters do not become components of the tissues, 

 but only of the fluids circulating through them ; and that 

 thus their metamorphosis is not an immediate result of the 

 organic activities. We know that their stability is such that 

 the thermal and chemical forces to which they are exposed 

 in the body, cannot alone decompose them. The only explan- 

 ation open to us, therefore, is that the transformation of these 

 oxy-hydro-carbons, into carbonic acid and water, is due to 

 communicated chemical action. 



§ 16. This chapter will have served its purpose if it has 

 given a conception of the extreme modifiability of organic 

 matter by surrounding agencies. Even did space permit,, 

 it would be needless to describe in detail the immensely 

 varied and complicated changes which the forces from mo- 

 ment to moment acting on them, work in living bodies.' 

 Dealing with biology in its general principles, it concerns us 

 only to notice how specially sensitive are the substances of 

 which organisms are built up, to the varied influences that 

 act upon organisms. And their special sensitiveness has been 

 made sufiiciently manifest, in the several foregoing sections. 



