86 



tlie views of evolutionists on the one hand or o£ believers in- 

 special creation on the other. Doubtless most of us have- 

 arrived at conclusions on these subjects ; but whatever those 

 conclusions may be, we shall all be ready to welcome a dis- 

 covery which will leave through all time a broad mark on the 

 historical records of scientific research, and confer lasting- 

 honours on those who have been engaged in bringing it to 

 light. Most of us know that another naturalist announced almost 

 simultaneously his independent discovery of the same fact. 

 "We are not at present informed when Mr. Caldwell arrived at 

 his conclusion ; but without wishing to withhold for one moment 

 any portion of the honour that is due to him, I claim for Dr. 

 Haacke priority as being the first to announce publicly his 

 discovery, and the first to exhibit at a meeting of a scientific 

 Society the eg(^ taken from the pouch of the echidna, by which 

 he was enabled to demonstrate the accuracy of his observations. 

 I venture on behalf of this Society to offer to our learned con- 

 frere our warmest congratulations. Some credit, too, is due to 

 our assistant Secretary (Mr. Molineux), who has been at work 

 for some months in obtaining specimens from Kangaroo Island 

 with the view of enabling naturalists in Adelaide to pursue 

 their investigations. 



I propose in the present address to bring under your notice 

 the influence of micro-organisms in the production and pro- 

 pagation of that class of diseases which are of an infectious 

 nature, or — to use the old-fashioned but not less expressive 

 word of our grandmothers — which are "catching." Most 

 members of this Society will be familiar with the fact that 

 Yarious animal parasites of a low type are known to live 

 and grow in animals of a much higher organization. The 

 papers read before the Society by Dr. Thomas on Hydatids, and 

 by Dr. Mann on the Blood Filaria, have informed us of the- 

 destructive effects of these parasites in the internal organs of 

 their host. In these cases we have to do with organisms of 

 comparatively large size. You will also remember that many 

 vegetable parasites exist and destroy living tissues, each after- 

 its own peculiar fashion. We find sarcina in the stomach, 

 oidiiim albicans in the mouth, ^^ndLtricTiophyton to7isurans in ring- 

 worm of the scalp and elsewhere. These, too — although the last 

 one will split a hair till it resembles a crossing-sweeper's broom 

 — are comparatively large, their effects are chiefly local, and they 

 do not produce constitutional disturbance. Some of these, 

 however, manifest a characteristic which, in the still lower or- 

 ganisms, is more distinctly marked. They have the property 

 of infection. Every schoolmaster is familiar with this in the 

 plague of ringworm so troublesome at times in our larger 

 schools. Passing from these to organisms which are more 



