170 PHYSIOLOGY OF ALIMENTATION. 



attributed solely to the activities of lipase-containing bac- 

 teria found here. . Since we have become acquainted with 

 the presence of lipase in the normal secretions of this viscus ; 

 this idea must be modified, and the two sources of li- 

 pase be taken into consideration. Mention must finally 

 be made of the cytase which certain of the intestinal bac- 

 teria contain. This ferment has the power of acting upon 

 cellulose and converting it into dextrin and glucose. 



From what has been said, therefore, it can readily be 

 seen that certain of the bacteria of the intestinal tract may 

 even be of service to the animal which harbors them, for 

 they produce changes in the alimentary contents not unlike 

 those brought about by the normal secretions, and in the 

 last example cited above, they may even render an other- 

 wise useless constituent of our food (the cellulose of the 

 vegetable cells) useful to the animal organism by convert- 

 ing it into substances which can be taken up by the body. 

 While these cytase-containing bacteria probably play only 

 an insignificant role in the digestive processes of the car- 

 nivora, the herbivora no doubt are dependent upon these 

 bacteria in no mean way, for even if the amounts of dex- 

 trin and glucose formed in the hours during which the bac- 

 teria are active are not very large, the dissolution of the 

 cellulose walls of the vegetable cells liberates their more 

 readily digestible contents and so puts these into a posi- 

 tion to be absorbed. 



So far as the amount of the just-described forms of diges- 

 tion of which the various bacteria are capable is concerned, 

 it is no doubt correct to say that as compared with the 

 activities of the normal secretions of the alimentary tract 

 this is, under ordinary circumstances, comparatively little. 



We come now to the bacterial decompositions in the ali- 

 mentary tract which are apparently of no service to the host 

 and which are at times of a distinctly injurious character. 

 It is these that have excited the greatest amount of medical 

 discussion and have led to the volumes of literature on in- 



