THE HYGIENE OF NUTRITION 357 



should be pointed out, lies in the peculiar attractive- 

 ness of meat rather than in its composition. Eggs, 

 beans, and peas might have as much to do with auto- 

 intoxication if they were as appealing to the average 

 appetite. 



It will be noted that we can avoid toxic decomposition 

 in the intestine either by keeping the tract as free as 

 possible from lagging residues or by controlling the 

 prevalent type of bacterial action. This latter pro- 

 cedure has had many advocates. It is taught that the 

 more harmful microorganisms can be kept from undue 

 increase if less objectionable species are deliberately 

 encouraged. This is the theory of the various sour-milk 

 treatments. The familiar change that takes place in 

 milk is a fermentation of milk-sugar with the formation 

 of lactic acid. Although lactic acid in the muscular 

 and nervous tissues of the body is clearly undesirable, 

 it seems that a good deal of it may be introduced into 

 the alimentary canal or produced there without ill 

 effects. Certain kinds of bacteria which form lactic 

 acid from sugars at a rapid rate can be isolated, grown 

 in quantity, and dispensed. 



The subject may prepare sour milk by means of these 

 cultures and drink it, swallowing the acid and the pro- 

 ducing organisms at once. Or he may prefer to swallow 

 the cultures together with some sugar which may then 

 be fermented within the tract. In proportion as this 

 type of fermentation becomes the dominant one certain 

 other decompositions are inhibited. It is a curious fact 

 that something can be learned about the state of the 

 colon by studying the urine. There are well-recognized 

 products of protein putrefaction that may be absorbed 

 into the circulation and later excreted in modified form 

 by the kidneys. The amount of these compounds in 

 the urine is thus an index of the extent of objectionable 

 decomposition in the lower part of the canal. Lactic 

 acid treatments often reduce the quantity of these tell- 

 tale substances. 



