MICRO-ORGANISMS AS PARASITES. 19 



thousands of years. This terrible disease, whose history I have 

 imperfectly described, is now known to be caused by a bacillus 

 which takes up its abode chiefly in the lymphatic vessels and the 

 deep tissues of the dermis. Not only is it never found in the 

 epidermis, but, as MM. Cornil et Suchard say, " the epidermal 

 covering forms a varnish impenetrable to the special parasite 

 of leprosy." Fortunately for us, the same may be said of the 

 epidermis, ivhen imi7ijicred, with regard to many other diseases. 



The anaesthesia characteristic of leprosy is found to arise from 

 enormous groups of cells, containing bacilli, which lie amongst the 

 peripheral nerve-endings. The bacilli also invade the epiglottis 

 and the thyroid cartilage, thus accounting for the peculiar 

 hoarseness of the voice in leprosy. The bacillus leprce, one of the 

 oldest and most fatal enemies of the human race, is an extremely 

 faint, slender rod about half the length of a human blood-corpuscle. 

 It closely resembles bacilhis tuberculosis, except in being slightly 

 wider in comparison to its length. Without staining, the bacilli 

 are so small and faint as to be unrecognisable. What incalculable 

 pains have been taken in discovering the properties of aniline 

 and other dyes in staining (and thereby revealing the existence of) 

 micro-organisms, can best be realised by those who have read 

 Koch's description of his discovery of the bacillus of Septiaxmia 

 in the mouse, an organism so small that it can swarm inside the 

 red blood-corpuscles of mice. By numberless patient and most 

 delicate experiments, it was found out that organisms otherwise 

 too small, colourless, and delicate to be visible by the strongest 

 powers of the microscope, became easily recognisable when 

 suitably stained ; each micro-organism having an affinity for 

 some particular dye. Moreover, the protoplasm of cells takes one 

 colour, the nucleus another, the cell-wall (in vegetable cells) a 

 third, and the bacilli, when present in the cells, a fourth. In 

 Neisser's experiments on the lepra bacillus, the ordinary cell 

 protoplasm was stained rose-eosin ; the nuclei were found to be 

 blue, whilst the protoplasm of cells which contained bacilli was 

 coloured a bright orange ; the bacilli, being less deeply stained, 

 were visible with a comparatively low magnifying power. 



With regard to the question of the contagiousness of leprosy, 

 I will quote the concluding words of MM. Cornil et Suchard, 



