268 DR. R. ANGUS SMITH ON THE 



from it in hygiene and meteorology. These results are 

 the great extension of the idea that ammonia may be an 

 index of decayed matter. The idea itself has been used 

 partly^ and to a large extent — as illustrated in my 'Air and 

 Rain ; ' the facts now to be given enable us to claim for 

 it a still more important place. The application seems to 

 fit well the conditions already examined; and by this 

 means currents from foul places have been readily found. 

 This does not apply to the substances which may be called 

 germs whether it be possible to see them or not, because 

 these are not bodies which have passed into the ammo- 

 niacal stage, although some of them may be passing — 

 those, for example, which are purely chemical and exert 

 what we may call idiolytic action. This word — from i8to9, 

 " its own (peculiar)," and \v(n^, ''decomposition'^ — may 

 serve to mark this peculiar action, which was left by Liebig 

 unnamed ; he used the vague term invented by Berzelius, 

 namely " catalytic." I have elsewhere recognized the two 

 classes of germs, instead of any disputed one, without 

 naming them. 



It is now many years since Liebig first surprised me by 

 saying that iron-ores and aluminous earths were capable 

 of taking up ammonia, and if they were breathed upon 

 we were able even to smell that substance. He, much 

 about the same time, made numerous experiments in order 

 to find the ammonia of the atmosphere, and to measure its 

 amoimt in rain. The result for science was great; and 

 Professor Way continued the inquiry for the Royal Agri- 

 cultural Society. Dr. Gilbert, F.R.S., amongst his many 

 labours in the department of agricultural science, has 

 made this inquiry into ammonia of rain in still later times ; 

 but I shall not at present quote his results, as this paper 

 is not intended to go fully into the subject, but rather to 

 look in a different direction. The first paper T ever read 



