42 POISONS : THEIR EFFECTS AND DETECTION. [§§ 31 , 32 . 
Researches on the action of the ipecacuanha alkaloids on amoeba 1 
have given the following definite results :—Emetine C 25 H 27 (OMe) 4 NH.N, 
cephaeline C 25 H 27 OH(OMe) 3 NHN,N-methylemetine C 25 H 27 (OMe) 4 NMeN, 
and N-methyl cephaeline C 25 H 27 OH(OMe) 3 NMeN were about equal ; 
that is to say that, with the nucleus intact, an hydroxyl in the place of 
a methoxyl group, or a methyl group displacing the hydrogen of NH, 
made no appreciable difference. On the other hand, psychotrine, which 
differs from cephaeline by the nucleus containing only two atoms of 
hydrogen, is almost inactive. Nor-emetine also, which differs from 
emetine by the replacement of the four methoxyl groups by four 
hydroxyls, has also much inferiority. 
§ 31. Stereochemical Influences. —Stereo-isomerides often show pro¬ 
found differences in physiological action; e.g., Z-hyoscyamine and 
Z-adrenaline are both far more active than the d - varieties. Similarly, 
of the two isomerides pilocarpine and iso-pilocarpine, the latter has only 
a fraction of the activity of the former. This diversity of effect is not 
confined to asymmetric carbon, but it is also seen in a and j8 metho- 
chlorides of canadine produced by the methylation of Z-canadine. The 
nitrogen in these two compounds is asymmetric, the j8 salt producing 
a curare effect on the muscles of the frog twelve times more powerful 
than the a salt. No generalisation with regard to stereo-isomerides can 
be made, because there are exceptions; e.g., d- and Z-homatropine and d-l- 
homatropine differ but little in mydriatic action. It is probable, from in¬ 
direct evidence, that the different physiological effects of stereo-isomerides 
are due to difference in the ability of one or other to combine with some 
proteid or constituent of the nerve cell. The j3 and e stereo-isomerides 
of cholestanol inhibit the haemolytic power of the saponins ; the j8 com¬ 
pound has this power to a marked degree, the e compound has but slight 
activity. The explanation is simple : the /bcholestanol combines with 
the saponin, such as digitonin, and the addition product is practically 
inert; while the e-cholestanol does not combine, and therefore does not, 
as it were, remove the saponin. 
§ 32. M. Ch. Michet 2 has investigated the comparative toxicity of 
the metals by experiments on fish, using species of Serranus , Grenolabrus , 
and Julius. The chloride of the metal was dissolved in water and 
diluted until just that strength was attained in which the fish would 
live 48 hours ; this, when expressed in grammes per litre, he called 
“ the limit of toxicity .” , 
The following is the main result of the inquiry, by which it will be 
seen that no relation was found between “ the limit of toxicity ” and the 
atomic weight. 
1 Pyman and Wenyon, J. Pharmac., 1917. 
2 “ De la Toxicite compare© des differents Metaux.” Note de M. Ch. Michet, 
Com.pt. Pend., xciii. 649, 1881. 
