president's addeess. 203 



tutes, if nothing more, an admirable working hypothesis, on the 

 truth of which much of the fabric of biological science, and 

 still more of the medical science of the future, almost entirely 

 depends. If the minute organisms which we believe to consti- 

 tute the virus of so many diseases are capable of arising de novo, 

 where are our hopes of being able to stamp out any of these 

 diseases, — where the use of those elaborate precautions which 

 we now take against the spread of them by direct contact or 

 atmospheric infection ? But before saying anything of these 

 smallest of microbes, let me attempt to epitomize some of the 

 knowledge which of late years we have gained respecting the 

 larger entozoa. 



Parasitic diseases, such as those resulting from the presence 

 of entozoa, — of which, perhaps, the most familiar example 

 is the tape-worm, — have been known and recognised, if not 

 thoroughly understood, from the very earliest times ; but the 

 life-histories of the various animals concerned, have for the 

 most part been unknown until a comparatively recent period. 

 These form certainly one of the most curious chapters in the 

 whole range of biological science. But amongst the earliest con- 

 tributions of microscopic investigation to practical medicine was 

 the discovery of the parasitic nature of ringworm and of the 

 fungus to which that disease is due. The hair, in this complaint, 

 is seen to be filled with a fungus which grows and reproduces 

 itself in the shaft of the hair itself with great rapidity, the hair 

 becoming brittle and breaking off very near the skin. The true 

 pathology of the disease having been thus ascertained, the treat- 

 ment of it became comparatively simple and certain, though 

 still in many cases sufiiciently troublesome. It is obvious that 

 the proper line of treatment is to destroy the parasite — an end 

 which may be attained by the use of various agents, into the 

 details of which I need not now enter. Nor shall I dwell at all 

 upon those only too numerous external insect parasites, which 

 are familiar to every one, which are commonplace in their his- 

 tory, and may usually be dealt with by short and easy methods. 



Let me, however, endeavour to place briefly before you the 

 present state of our knowledge as regards some of the more 



