( J.^2 ) 



mctlivl alcolidl (I.OOO.OH iu<ir. 



formic acid (I.OOO.j^ iiiüt. 



acetone O.ÜOO.OOB mgv. 



camplior 0.0()0.()()().()()9.fi mgr. 



ioiioii ().()()().()( )().<)( )().() 19 ni.oT. 



Let lis restrict (nirsclves to tlicsc suhslaiices lor llie present. Wlieii 

 fiiUy oxidised tliey are converled iiilo tl, O and VO^. Hence llieir 

 products of coniWiisiioii may \)o considered as enlirely indilferenl 

 additions to tlie cell-substance if they are j)rodnced gradually and 

 in small ((uaidilies. If we regard smell as an inlra-molecular pro|)erty, 

 which is |)roI)able for these substances (leaving it an oi)en question 

 whether foi' substances containing atoms like S, As, etc. smell 

 uuiy ])erhaps dei)end on intra-atomic conditions), the (|uaiitily of 

 energy involved in an olfactory stimulus will ne\er exceed tli(> heat 

 of combustion. 



For the four tirst-mentioned std)stances the heal of coud)ustiou is 

 kiio\NU and auu)uiits to 5.7, J. 5, 7.5 and 9.3 gram-calories |)er milli- 

 gram respectively; that of iouon is uidvuown, but may be estimated 

 at 9.(j gram-calory. Theji the quantities of energy involved here 

 (for the anu)unt of smelling substance contained in 0.2 cc.) are for: 



methyl-alcohol 14443 ergs 



formic acid 74(10 ,, 



acetone 25'20 ,, 



canq)hor 3.9 ,, 



iouon O.OO.S .. 



Attenq)ts made in ordei' lo iiiid oiil how much of these smelling 

 substances is absorbed iu llie oltacloi-y mucous mendiraue were 

 hitherto uusuccessfid. Neither in oil, nor iu Jierve-substaiice we were 

 able to detect an appreciable (puintily of iouon, after they had 

 been left in contact for some time with an atmosphere of ioiu)U. 

 Pi-esumably vei'y little is absorbed. Moreover it follows from the 

 remai'kably dilferent degree iu which chemically related substances 

 show smelling power ^) that only an extremely small part of the 

 intra-molecular energy displays any olfacto-chemical etfect. So we 

 are justitied iu assuming that here also the minimum stimulus in 

 the nerve-terminal will later api»ear to be of the order of the light- 

 stimulus or even smaller. 



1) Onder/.oekingpn Pl\ysiol. Lai), d. Utroclit.sclio Hoogescliool (.5) IV. p. 232. 

 Chloiol'oi'm, bromoform, iodoiüini have a specific smelling-power of which the 

 mutual ratio is as 1 : 69 : 153 24. 



