Immunity of the skin and mucous membranes 409 



even distilled water, gave the same result. In all these cases it is 

 evident that, in the tears, there is no bactericidal cytase comparable 

 with that found in the serums and other body fluids which may 

 contain this phagocytic diastase. The experiments with heated tears 

 demonstrate this clearly. On the other hand, these same experiments 

 lead one to suppose that the diminution and even the disappearance [429] 

 of the micro-organisms in the tears, is due to a large extent, and 

 perhaps completely, to an agglutinative action of the salts, a fact 

 which has been demonstrated by several observers. 



In all these cases it is indisputable that the mechanical part 

 played by the tears is the most important of the defences offered 

 by the conjunctiva of the eye against the microbial invasion. That 

 this defence is not always sufficient is proved by the frequency of 

 conjunctivitis, as well as by the ease with which certain micro- 

 organisms, inoculated into the conjunctival sac, set up a general 

 infection. This is specially the case with the coccobacillus of 

 human plague. When it is introduced into the conjunctival sac 

 of susceptible animals (rat, guinea-pig, &c.), it passes thence into 

 the nasal cavity and soon produces a generalised and fatal infection. 

 The conjunctival membrane, even when perfectly intact, readily 

 absorbs certain poisons. Everyone knows the rapidity with which 

 atropin, when introduced into the conjunctival sac, causes dilatation 

 of the pupil. But the mucous membrane may serve also as the 

 port of entry for toxins of microbial origin. Several observers, 

 and especially Morax and Elmassian 1 , have demonstrated that the 

 diphtheria poison placed upon an unbroken conjunctival membrane, 

 where the epithelial layer is uninjured, sets up local lesions which 

 progress very slowly but which terminate in the formation of actual 

 false membranes. Nevertheless, it must be admitted that the intact 

 epithelial layer of the conjunctiva exerts a certain defensive action 

 against the penetration of toxins, although a very slight lesion of this 

 layer will allow of the ready absorption of the diphtheria poison and 

 the formation of false membranes. 



The cornea likewise, so long as it is intact, exhibits a marked 

 resistance against the penetration of micro-organisms and of toxins. 

 When it becomes injured in any way its epithelium is repaired with 

 great rapidity, as has been well demonstrated by Ranvier 2 , who has 

 shown that the walls of the wound close by a process of epithelial 



1 Ann.de Hnst. Pasteur, Paris, 1898, t. xn, p. 210. 



2 Arch, d'anat. microsc., Paris, 1898, t. n, pp. 44, 177. 



