HYDROCYANIC ACID. 
211 
§ 263.] 
to produce a lethal dose for an adult; with children less—in fact, 4 to 
6 bitter almonds are said to have produced poisoning in a child. 
§ 263. Action of Hydric and Potassic Cyanides on Living Organisms. 
—Both hydric cyanide and potassic cyanide are poisonous to all living 
forms, vegetable or animal, with the exception of certain fungi. The 
cold-blooded animals take a larger relative dose than the warm-blooded, 
and the mammalia are somewhat more sensitive to the poisonous action 
of the cyanides than birds ; but all are destroyed in a very similar 
manner, and without any essential difference of action. The symptoms 
produced by hydric and potassic cyanide are identical, and, as regards 
general symptoms, what is true as to the one is also true as to the other. 
There is, however, one important difference in the action of these two 
substances, if the mere local action is considered, for potassic cyanide is 
very alkaline, possessing even caustic properties. For instance, the 
gastric mucous membrane of a woman, who had taken an excessive dose 
of potassic cyanide on an empty stomach, was so inflamed and swollen 
that its state was similar to that induced by a moderate quantity of 
solution of potash. On the other hand, the acid properties of hydric 
cyanide are very feeble, and its effect on mucous membranes or on the 
skin in no way resembles that of the mineral acids. 
It attacks the animal system in two ways : the one, a profound 
interference with the ordinary metabolic changes ; the other, a paralysis 
of the nervous centres. Schonbein discovered that it affected the blood 
corpuscles in a peculiar way ; normal blood decomposes with great ease 
hydrogen peroxide into oxygen and water. If to normal venous blood 
a little peroxide of hydrogen be added, the blood at once becomes bright 
red ; but if a trace of prussic acid be present, it is of a dark brown 
colour. The blood corpuscles, therefore, lose their power of conveying 
oxygen to all parts of the system, and the phenomena of asphyxia are pro¬ 
duced. Geppert 1 has proved that this is really the case by showing, in a 
series of researches, that, under the action of hydric cyanide, less oxygen is 
taken up, and less carbondioxide formed than normal, even if the percent¬ 
age of oxygen in the atmosphere breathed is artificially increased. The 
deficiency of oxygen is in part due to the fact that substances like lactic 
acid, the products of incomplete combustion, are formed instead of C0 2 . 
At the same time the protoplasm of the tissues is paralysed, and 
unable to take up the loosely bound oxygen presented. This explains a 
striking symptom which has been noticed by many observers, that is, if 
hydrocyanic acid be injected into an animal, the venous blood becomes 
of a bright red colour ; in warm-blooded animals this bright colour is 
transitory, but in cold-blooded animals, in which the oxidation process is 
slower, the blood remains bright red. 
1 Geppert, Ueber das Wesen der CNH-Vergift; mil einer Tafel , Berlin, 1889 ; 
Sep.-Abdr. aus Ztschr. f. klin. Med., Bd. xv. 
