BY R. GREIG SMITH. 155 



experimental animal, enabling it to attack and dissolve more viru- 

 lent bacteria of the same kind. Thus immunity against one 

 microbe is begotten, as it were, by the previous digestion in the 

 tissues of the same micro-organism, and a multiplicity of immune 

 substances can only be obtained by the previous lysis of a diver- 

 sity of bacteria. In a young animal this must occur. 



In ^yriting upon the question of bovine and human tuberculosis, 

 Behring appears to say : — " The freedom with which milk-bacteria 

 find their way through the walls of the alimentary tract into the 

 circulation, owing to the incomplete continuity of the epithelium 

 and absence of active ferment secretion in youDg animals, makes 

 the disposition to tuberculous infection entirely physiological and 

 normal."* Without discussing the particular case of tuberculous 

 infection, does it not seem possible that the non-continuity of the 

 epithelium of the alimentary tract of young animals is the means 

 by which an all wise Providence endeavours to accelerate the for- 

 mation of protective bodies before the immunity bestowed upon 

 them by the parents has become exhausted 1 



We have seen that all investigators do not admit the passage 

 of bacteria through the uninjured intestinal wall, for the reason 

 that bacterial growths cannot always be obtained when portions 

 of the organs or membrane are sown in nutritive fluids. The 

 cause of this failure will l)e apparent if we assume that they are 

 capable of passing through. In doing so, they will be attacked 

 either there or in the more remote tissues, first, in the case of 

 the young animal, by the maternal, then by the individual immune 

 substances. During the lysis of these microbes the cells will be 

 trained or stimulated to produce more immune bodies. It is also 

 possible that the presence of bacteria in the intestinal tract causes 

 the cells of the mucous membrane to secrete immunity enzymes 

 which diffuse not only into the lumen, but also throughout the 

 membrane. The diversity of bacteria produces a variety, and 

 the continued solution of organisms will induce the formation of 

 a quantity of immune substances. The quantity and the hetero- 



* Nature, June 6th, 1904, p. 126. 



