——— a 
NovEMBER gy, 1916] 
to isolate it completely and to carry out its analysis. 
For example, the substance known now as tryptopuane 
was known to occur in certain substances and not in 
others long before Hopkins succeeded in presenting it 
in pure form. And in the same way it may be possible 
to determine the presence or absence of substances in 
living tissues, and even some of their properties, through 
their reaction to chemical reagents—tnat is, through 
the study of the pharmacology of these tissues. I do 
not claim that pharmacological investigation can at 
present do much more than the qualitative testing of 
the tyro in the chemical laboratory, but even a small 
advance in the chemistry of living matter is worthy of 
attention. 
All forms of living matter to which they. have free 
access are affected by certain poisons, and some of 
these have obvious chemical properties which suggest 
the method of their action; thus the effects of alkalies 
and acids and of protein precipitants scarcely need 
discussion. Others, such as quinine and prussic acid, 
which also affect most living tissues, have a more 
subtle action. Here it is believed that the common 
factor in living matter which is changed by these 
poisons is the ferments, and quinine and prussic acid 
may therefore be regarded as qualitative tests for the 
presence of some ferments, notably those of oxidation, 
and, in fact, have been used to determine whether a 
change is fermentative in character or not. 
In other poisons the action on the central nervous 
system is the dominating feature, and among these 
the most interesting group is that of the simple bodies 
used as anzsthetics and hypnotics, such as ether, 
chloroform, and chloral. The important use of this 
group in practical medicine has perhaps obscured the 
fact that they act on other tissues besides the central 
nervous system, though we are reminded of it at too 
frequent intervals by accidents from anesthesia. But 
while they possess this general action, that on the 
nervous tissues is elicited more readily. Not only the 
nerve-cell, but also the nerve-fibre react to these 
poisons, as has been shown by Waller and others. 
And even the terminations are more susceptible than 
the tissues in which they are embedded, according 
to the observations of Gros. The selective action on 
the nervous tissues of this group of substances has 
been ascribed by Overton and Meyer to the richness 
in lipoid substances in the neurons, which leads to the 
accumulation of these poisons in them, while cells 
containing a lower proportion of lipoid are less affected. 
In other words, Overton and Meyer regard these drugs 
as a means of measuring the proportion of. lipoids 
in the living cell. This very interesting view has been 
the subject of much discussion in recent years, and, 
in spite of the support given it by several ingenious 
series of experiments by Meyer and his associates, no 
longer receives general acceptance. Too many excep- 
tions to the rule have to be explained before the action 
of these bodies can be attributed wholly to their co- 
efficients of partition between lipoids and water. At 
the same time, the evidence is sufficient to justify the 
statement that the property of leaving water for lipoid 
is an important factor in the action of the bodies, 
although other unknown properties are also involved 
in it. And whatever the mechanism of the character- 
istic action, these substances in certain concentrations 
may be regarded as tests for the presence of nervous 
structures, and have been employed for this purpose. 
More interest has been displayed in recent years in 
the alkaloids which act on the extreme terminations 
of various groups of nerves. These are among the 
most specific reagents for certain forms of living matter 
which we possess. Thus, if an organ reacts to adrena- 
line, we can infer that it contains the substance char- 
acteristic of the terminations of sympathetic fibres 
with almost as great certainty as we infer the presence 
NO. 2454, VOL. 98] 
NATURE 
system. 
201 
of a phenol group trom the reaction with iron. And 
this sympathetic substance can be further analysed 
into two parts by means of ergotoxine, which reacts 
with the substance of the motor sympathetic ends, 
while leaving that of the inhibitory terminations un- 
ffected. Similarly, the endings of tne parasympathetic 
nerves are picked out with some exceptions by the 
groups represented by atropine and pilocarpine, and 
here again there must be some detinite substance 
which can be detected by these reagents. 
Further, some light has been thrown on, at any 
rate, one aspect of these nerve-end substances by the 
observation that they all react to only one optical 
isomer in each case. Thus the dextrorotatory forms 
are ineffective in both atropine and adrenaline, and 
this suggests strongly that the reacting body in the 
nerve-ends affected by these is itself optically active, 
though whether it bears the same sign as the alkaloid 
is unknown. This very definite differentiation between 
two optical isomers is not characteristic of all forms. 
of living matter. For example, the heart muscle 
seems to react equally to both levo- and dextro- 
camphor. The central nervous system contains sub- 
stances which react somewhat differently to the 
isomers of camphor and also of atropine, but the con- 
trast is not drawn so sharply as that in the peripheral 
nerve-ends. 
The tyro in the chemical laboratory is not often 
fortunate enough to be able to determine his analysis 
with a single test. He finds, for example, that the 
addition of ammonium sulphide precipitates a consider- 
able group of metals, which have then to be distin- 
guished by a series of secondary reactions. The 
pharmacologist, as an explorer in the analysis of living 
matter, also finds that a single poison may affect a 
number of structures which appear to have no anatom- 
ical or physiological character in common. But as the 
chemist recognises that the group of metals which 
react in the same way to his reagent have other points 
of resemblance, so perhaps we are justified in consider- 
ing that the effects of our poison on apparently different 
organs indicate the presence of some substance or of 
related substances in them. A great number of in- 
stances of this kind could be given, and in many of 
these the similarity in reaction extends over a number 
of poisons, which strengthens the view that the differ- 
ent organs involved have some common reacting sub- 
stance. 
One of the most interesting of these is the common 
reaction of the ends of the motor nerves in striated 
muscle and of the peripheral ganglia of the autonomic 
It has long been known that curare and its 
allies act in small quantities on the terminations of 
the motor nerves in ordinary muscle, while larger 
amounts paralyse conduction through the autonomic 
ganglia. These observations appear to leave no ques- 
tion that there is some substance or aggregate common 
to the nerve-ends in striated muscle and to the auto- 
nomic ganglia. Other analogies exist between the 
ganglia and the post-ganglionic terminations of the 
parasympathetic, as is shown by their reactions to 
the tetramethyl ammonium series; between the heart 
muscle and the cardiac inhibitory centre, as shown by 
digitalis and aconitine ; between kidney-cell and ordinary 
muscle, as shown by caffeine and other purine bodies. 
Many other examples might be cited in which organs 
which are apparently not related, either morphologic- 
ally or in function, react to poisons in quantities which 
are indifferent to the tissues in general. And this 
reaction in common can only be interpreted to mean 
that there is some substance or group of related sub- 
stances common to these organs. The reaction may 
differ in character; thus a drug which excites one 
organ to greater activity may depress another, but the 
fact that it has any effect whatever on these organs 
