iv DIGESTION IN THE INTESTINE 223 



secreted by the stomach and the amount of sodium carbonate 

 secreted by the intestine. 



To this sodium carbonate Bunge assigns yet another function. 

 As -fast as it is secreted, it diffuses in the acid mass of the intes- 

 tinal contents, leading to a fresh formation of sodium chloride, with 

 evolution of free carbonic acid, which makes the whole mass 

 spongy and permeable to the pancreatic juice, thus assisting the 

 digestion or solution of the food-stuffs. 



IV. To the chemical action of the secretions poured into the 

 intestine during digestion, must be added the constant action, 

 'even under normal conditions, of the Bacteria that inhabit the 

 intestine. 



Their presence in the intestinal contents has been known ever 

 since the microscope was first applied to the phenomena of life 

 (Leeuwenhoek). The problem of determining their true physio- 

 logical significance is, however, beset with difficulties, and we can- 

 not at present claim that any definite theory has been arrived 

 at. We must here confine ourselves to a very general survey of 

 the subject. 



There can be no doubt that the bacteria of the intestine pene- 

 trate from outside, along with the food, the fluids, the air that we 

 swallow; and that the development of the gases within the 

 intestines, as well as a considerable part of the substances that 

 compose the faeces, are due to the fermentations they excite, and 

 the further putrefactive decomposition which they produce in the 

 food-stuffs partially digested by the enzymes. We know, in fact, 

 that during the whole foetal period up to birth, there is no 

 fermentation in the intestine, which is sterile and destitute of 

 faeces. With the first frothy saliva, i.e. that mixed with air- 

 bubbles, swallowed with the milk by the new-born infant, the first 

 organic germs are introduced into its body. Many of these are 

 destroyed by the acidity of the gastric juice, but others pass into 

 the intestine, where they excite fermentative processes with 

 evolution of gas. 



It is evident that the bacteria introduced with the food and 

 drink must be the same which act in the open air on the ferment- 

 able and putrescible matters. From the intestine of the new-born, 

 that have sucked milk, very few kinds of bacteria are, however, 

 secreted with the meconium in the 4th-10th hours after birth 

 (Escherich, 1875). All the other germs have been destroyed by 

 the bactericidal action of the gastric juice, or fail to find the 

 necessary conditions of their existence in the intestine of the 

 sucking infant. 



In adults, too, although an enormous variety of germs con- 

 tinually pass by the mouth into the gastro-intestinal tube, the 

 gastric bacteria consist almost exclusively of Blastomycetes and 

 Sarcinae, organisms accustomed to live in an acid medium, and 



