48 MICROBES AND TOXINS 



intestine, but that is not the rule and can only be produced by 

 administering the dust in large quantities in rapid succession : 

 these are artificial and exceptional, not natural, conditions. It 

 is the same in the case of bacteria. In an animal in perfect 

 health they do not penetrate the intestinal wall, but they can 

 be made to do so under the influence of fasting and fatigue 

 (experiments of Ficker). One may say that their passage is 

 the first and a very early sign of an agonal phenomenon, an 

 anticipation of that exodus of bacteria which occurs immed- 

 iately after death. 



We must not forget, however, that, according to the state- 

 ments of Porcher and Desoubry, bacteria pass from the 

 intestine into the blood each time the animal digests, and that 

 to get sterile sera it is necessary to bleed anti-diphtheria and 

 anti-tetanus horses only during the intervals between digestion. 



The question is less simple than it looks, because the mucous 

 membrane is quite as active as, if not more so than, the 

 bacteria. Not only is it built up of active living cells, but there 

 are continually traversing it other living motile cells, the 

 leucocytes, which play an active part in the phenomena of 

 digestion and absorption, of defence and of resistance. 



The cellular mechanism of defence does not invalidate the 

 conclusion of this chapter. Being useless for digestion, and a 

 constant cause of putrefaction, the intestinal flora is a perman- 

 ent source of danger for the body. The intestinal flora 

 represents in our interior the external world with its unregulated 

 fermentations only limited by their mutual competition. It 

 represents in the interior of our bodies the innumerable legions 

 of bacteria in nature, which find their pabulum and their prey 

 in fermentable material of every kind, and which are as eager 

 to attack the proteins and carbohydrates of our living tissues 

 as to attack the sugar and the casein of fermenting milk. The 

 power of resistance of the body is counterbalanced by its 

 sensitiveness towards the poisons which are being continually 

 secreted, and which are capable at least of accelerating the 

 approach of old age if not of directly causing death. 



Researches on the intestinal flora are bound to take a 



