110 INDUCTION SHOCKS 
was stronger than in the second, whereas, if reliance were placed upon 
the results given when the high additional resistance was in circuit, it 
would appear that the second stimulus was more than twice as strong 
as the first. The subjoined tabulation will serve to emphasize the 
error: 
First 
Z (tissue only) 
6 6 
Z (70,000 g 
ohms added) 
16 8 41 
Second 
6 i 
do <\ 3 d 
Ratio of ist to 2d... 
i. 08 
0.41 I.I 
In determining specific stimulation values by means 
ZA 
of the expression /3 = -= - > particularly when the 
J\. ~\~ A. 
tissues stimulated have high resistances, errors in de- 
termining the value of A may easily vitiate the results. 
It will usually be found desirable to determine values of 
Z for at least three secondary resistances in addition to 
the tissue resistance itself. If the values of Z thus 
obtained are plotted against their respective resistances 
the curve which they yield reveals at once whether 
errors have been made in the determinations. The 
curve should be a straight line, cutting the ordinate for 
zero resistance at some point above the base line. Minor 
errors may be allowed for by drawing the curve to make 
them balance one another. This precaution is unnec- 
essary when tissues of low resistance are studied, since 
with them small errors in determining A are less sig- 
nificant. 
These are among the less obvious sources of error in 
