POISONS : THEIR EFFECTS AND DETECTION. 
[§ 35- 
the greater the pressure. The tube with the glass rod is horizontal, and a few mm. 
higher than the level of the fluid in R ; the zero point of the manometer is carefully 
adjusted to this level. If, in the manner stated, the pressure is raised, the pressure 
tube S begins to fill with the nutrient fluid, and the heart is compelled to work at a 
gradually increasing pressure, and this pressure may be registered on the kymograph 
by comparison of the tracing with that of the “ time curve ” Z. 
Jacobi has experimented with the pressures in the aorta and the auricle of large 
frogs, and has been able to nearly imitate the natural pressure in the isolated heart. 
If the latter works with a difference in level of 10-20 mm. the ventricle drives the 
fluid into the pressure tube 50-66 cm. and the fluid drops into the little syphon V 
regularly with each systole, two or three drops escaping, that is, with ten pulsations 
from 10-1 -5 grms., which with a height of 50 cm. corresponds to work of 50-75 grms. 
Jacobi ingeniously registers graphically the amount of fluid flowing in relation 
to time, pressure, and pulse as follows :—Around the little glass rod is wound a moist 
shred of wool, leading the liquid into a small glass vessel syphon-shaped, V, which is 
balanced at one end of a slender rod g, equilibrium being obtained by a counterpoise ; 
the little vessel when full rapidly empties itself by syphon action, and hence is in 
intermittent vibration ; these vibrations are recorded graphically by breaking and 
making contact at p with a galvanic battery arrangement, and by means of the 
magnet at M the attached marker draws a line on the revolving cylinder C, at the 
same moment lines are drawn by the markers A and Z. By means of this instrument 
either normal or poisoned fluid may be put into the isolated heart, and the effects 
thus graphically registered. 
§ 35. The Effect of Poisons on the Iris. —Several poisons affect the pupil, causing 
either contraction or dilatation. The most suitable animal is the cat, the pupil of 
the cat readily showing either state. 
Toxic Myosis, or Toxic Contraction of the Pupil. —There are two forms of toxic 
myosis, one of which is central in its origin. In this form, should the poison be 
applied to the eye itself, no marked contraction follows ; the poison must be swallowed 
or injected subcutaneously to produce an effect. The contraction remains until death. 
The contraction in such a case is considered to be due to a paralysis of the dilata¬ 
tion centre ; it is a myosis paralytica centralis ; the best example of this is the con¬ 
traction of the pupil caused by morphine. 
In the second case the poison, whether applied direct to the eye or entering the 
circulation by subcutaneous injection, contracts the pupil; the contraction persists 
if the eye is extirpated, but in all cases the contraction may be changed into dilatation 
by the use of atropine. An example of this kind of myosis is the action of muscarine. 
It is dependent on the stimulation of the ends of the nerves which contract the pupil, 
especially the ends of the nervus oculomotorius supplying the sphincter iridis ; this 
form of myosis is called myosis spastica periphera. A variety of this form is the myosis 
spastica muscularis, depending on stimulation of the muse, sphincter iridis, seen in 
poisoning by physostigmine. This causes strong contraction of the pupil when locally 
applied ; the contraction is not influenced by small local applications of atropine, but 
it may be changed to dilatation by high doses. Subcutaneous injection of small doses 
of physostigmine does not alter the pupil, but large poisonous doses contract the pupil 
in a marked manner. 
Toxic Mydriasis, or Toxic Dilatation of the Pupil. —The following varieties are 
to be noticed :— 
1. Toxic doses taken by the mouth or given by subcutaneous injection give rise 
to strong dilatation ; this vanishes before death, giving place to moderate contraction. 
This form is due to stimulation of the dilatation centre, later passing into paralysis. 
An example is found in the action of aconite. 
2. After subcutaneous or local application, a dilatation neutralised by physostig¬ 
mine in moderate doses. This is characteristic of /btetrahydronaphthylamine. 
3. After subcutaneous injection, or if applied locally in very small doses, dilatation 
occurs persisting to death. Large doses of physostigmine neutralise the dilatation, 
but it is not influenced by muscarine or pilocarpine : this form is characteristic of 
atropine, and it has been called mydriasis paralytica periphera. 
