1967] 
Eisner j Alsop & Eisner — -Defense Mechanisms 
1 1 1 
a millipede), the amount of this unknown can be calculated by 
titrating the remaining silver iodide to a clear end point. 
Text-figure 3 shows the apparatus in which individual millipedes 
were electrically stimulated to discharge and the emanating vapors of 
hydrogen cyanide were trapped for subsequent assay. A millipede 
was transferred into chamber A, and the two grid electrodes (e), 
whose shafts fit movably through the stoppers at the ends of the 
chamber, were gently pressed against the animal (m) from both 
sides. Three electric shocks (0.5 v., 25 Hz.) of 30 sec. duration, 
administered at 10 min. intervals, caused the millipede to discharge 
its secretion 2 . A pump circulated the gas in the system directing it first 
through one of two alternative pathways (I, II) bearing a cyanide 
trap (B) with a measured amount of standardized silver iodine sus- 
pension 3 , and then through a vessel (C) containing aqueous sulfuric 
acid, which prevented ammonia vapors, flushed from B, from reach- 
ing and harming the millipede. Since a single trap rarely sufficed to 
collect all the hydrogen cyanide emitted, the gas was bubbled through 
a series of traps. This involved routing the flow in alternate suc- 
cession through I and II, and replacing the individual traps with 
fresh ones for as long as their tendency to clear indicated the con- 
tinuance of cyanogenesis. As a rule, cyanogenesis came to a halt 
within 30 to 50 minutes, but in animals of high yield it often lasted 
beyond the hour. The final assay consisted of pooling the contents 
of all traps, and titrating away the residual turbidity with m stand- 
ardized solution (0.0 1 M) of sodium cyanide. The end point of the 
titration was determined photometrically (Bausch & Lomb Spectronic 
20 Spectrophotometer, set at A == 500) j by comparison with distilled 
This triple stimulus was adopted as a standard after it was demonstrated 
(by preliminary tests in which individual Apheloria were subjected to one 
or more shocks of varying intensity, frequency, and duration, and assayed 
for hydrogen cyanide production after each shock) that it was adequately 
strong to cause the animal to expel its entire secretory reserves. As a 
rule, the first shock sufficed to cause depletion or near depletion of the 
glands, which discharged visibly and usually simultaneously within seconds 
after onset of the stimulus. The second and third shocks evoked at most 
a very slight additional output of cyanide, indicating that the unexpelled 
residue had been minimal. Fourth shocks always proved superfluous. 
Specimens dissected after electric stimulation had empty glandular reser- 
voirs. The electric shocks did not noticeably harm the millipedes, which 
survived as long as untreated controls (usually from two to five months). 
The suspension was prepared from silver nitrate (0.001M), concentrated 
aqueous ammonia ( ca . 25%), potassium iodide (0.005M), and distilled 
water, mixed in the ratio of 10 : 2 : 1 : 87 by volume; 1 ml of this sus- 
pension is cleared by 5.4 /*g hydrogen cyanide. 
