(^7 
ever, to hold them upright, as might at tirst be supposed. They may 
be tilted to a greater angle than 45° without danger of the duid 
running out. 
Each glass barrel is numbered Avith the number of the experiment 
or of the animal to receive the injection. This is coiiAmnient and 
avoids confusion. 
The S 3 ndnges are prepared and filled in a special room where the 
exact measuring is done, and the rack is then found hand}" to carry the 
syringes to the animal room where the work of injection is carried on. 
In using this method in standardizing diphtheria antitoxin it is very 
important to shake and roll the syringe very actively so as to obtain 
an intimate mixture of the toxine with the serum. 
The toxine is first measured into the syringe barrel, then the diluted 
serum. The tAvo are thoroughly mixed by agitating the syringe and 
the mixture alloAved to stand at room temperature in diffused light one 
hour before it is inoculated into the guinea pig. 
The dilutions' are so arranged that the guinea pig always receives a 
total of 4 c. c. of fluid, thereby insuring constant pressure effects. 
We ahvays dilute our serums so that the amount of antitoxin desired 
will be contained in just 1 c. c. of the dilution. It is preferable to 
dilute the toxines so that the amount of desired poison Avill be con- 
tained in 2 c. c- or less of solution. In this w"ay Ave haA"e at least 1 c. c. 
left to make up the total of 4 c. c. Avitli Avhich to wash out the syringe 
barrel. 
THE GUINEA PIG. 
In this work much depends upon the guinea pig. Animals some- 
times shoAv such marked idiosyncracies in their reaction to certain 
poisons that it is remarkable in case of diphtheria toxine that a guinea 
pig should show comparatively little of this individuality. It may be 
stated in general terms that the guinea pig as a A"ital factor in the 
standardization of diphtheria antitoxin is quite as dependable as our 
ordinary Aveights and measures. 
It is of course necessary to use pigs under standard or normal con- 
ditions, of a deflnite weight, and approximately the same age. They 
should be bred from reliable stock, and fed and caged so as to insure 
vigorous animals. 
In order to meet all the exacting requirements Ave raise our own 
guinea pigs, thus insuring animals of reliable and constant conditions. 
Our pigs are fed upon oats and green food such as cabbage, carrots, 
and grass in season. 
Theobald Smith " has recently shown that some female guinea pigs 
give birth to progeny all of Avhich seem to shoAv a marked resistance 
« Smith, Theobald: Degrees of susceptibility to diphtheria toxin among guinea 
pigs. Transmission from parent to offspring. Jour. med. res., a". 13 (3), p. 341. 
