212 POISONS : THEIR EFFECTS AND DETECTION. [§§ 264 , 265 . 
§ 264. Effect of Prussic Acid on Lower Organisms.— In 1 to 
430 dilution prussic acid annihilates the function of Drosera. In 1 per 
1000 infusoria soon die, algae live longer. In a certain degree of dilution 
yeast-cells are paralysed but not killed, for on removal to a nutrient 
fluid, free from the acid, their activity is resumed. 
§ 265. Symptoms observed in Animals. —The main differences 
between the symptoms induced in cold-blooded and warm-blooded 
animals, by a fatal dose of hydric cyanide, are as follows :— 
The respiration in frogs is at first somewhat dyspnoeic, then much 
slowed, and at length it ceases. The heart, at first slowed, later contracts 
irregularly, and at length gradually stops ; but it may continue to beat 
for several minutes after the respiration has ceased. But all these 
progressive symptoms are without convulsion. Among warm-blooded 
animals, on the contrary, convulsions are constant, and the sequence of 
the symptoms appears to be—dyspnoea, slowing of the pulse, giddiness, 
falling down, then convulsions with expulsion of the urine and fseces ; 
dilatation of the pupils, exophthalmus, and finally cessation of the pulse 
and breathing. The convulsions also frequently pass into general 
paralysis, with loss of reflex movements, weak, infrequent breathing, 
irregular, quick, and very frequent pulse, and considerable diminution 
of temperature. 
The commencement of the symptoms in animals is extremely rapid, 
the rapidity varying according to the dose and concentration of the acid. 
It was formerly thought that the death from a large dose of the con¬ 
centrated acid followed far more quickly than could be accounted for 
by the blood carrying the poison to the nervous centres ; but Blake was 
among the first to point out that this doubt was not supported by facts 
carefully observed, since there is always a sufficient interval between the 
entry of the poison into the body and the first symptoms, to support the 
theory that the poison is absorbed in the usual manner. Even when 
Preyer injected a cubic centimetre of 60 per cent, acid into the jugular 
vein of a rabbit, twenty-nine seconds elapsed before the symptoms 
commenced. Besides, we have direct experiments showing that the acid 
—when applied to wounds in limbs, the vessels of which are tied, while 
the free nervous communication is left open—only acts when the ligature 
is removed. Magendie describes, in his usual graphic manner, how he 
killed a dog by injecting into the jugular vein prussic acid, and “ the 
dog died instantly , as if struck by a cannon ball,” but it is probable that 
the interval of time was not accurately noted. A few seconds pass very 
rapidly, and might be occupied even by slowly pressing the piston of 
the syringe down, and in the absence of accurate measurements, it is 
surprising how comparatively long intervals of time are unconsciously 
shortened by the mind. In any case, this observation by Magendie has 
not been confirmed by the accurate tests of the more recent experi- 
