71 
sides of the s^^ringe, is in turn forced under the skin. Care to avoid 
the injection of an unnecessaiy amount of air should be taken. 
The inoculation should be done rapidly and without unnecessary 
violence, which may affect the results. A trained assistant will hold 
the guinea pig, Avithout causing struggling, and an experienced oper- 
ator will cause little pain other than the prick of the needle through 
the skin. 
Care must of course be taken in inoculation that none of the ffuid 
escapes. We do not attempt to disinfect the skin. 
Effect upon the guinea 2>Hf - — After inoculation the guinea pigs are 
kept two in a cage and not disturbed until the seA^enth daA". Keeping 
man}" animals together in a pen may giA"e irregular results, because 
the strong and lusty pigs worry the sick ones and may hasten their 
end. Examining the pigs too often or too roughly must also be 
avoided. Theobald Smith believes that palpating the edema, caused 
by the reaction of the toxine at the site of inoculation, may cause the 
poison to break beyond the confines nature is setting up as a barrier, 
and may thus hasten the result. We haA"e found that there is little to 
be learned in AA-eighing or examining pigs during the first week, and 
we therefore leaA"e them undisturbed during this time. TheA" are 
Aveig'hed on the seA^enth daA" and each week following until the fourth 
Aveek, Avhen, if gaining Aveight and in good condition, they are passed 
from observation. 
Guinea pigs that show late effects of toxone^ as indicated by paral- 
ysis, Avill do so some time after the fourteenth day and before the 
thirtieth day Avith great regularity. The facts of paralysis^, sloughs, 
ulcers, etc., are carefully noted on the records. 
When an animal dies an autopsy is ahvays made in order to insure 
that the lesions are typical, and to guard against the possibility of 
infections — pneumonia, tuberculosis, pseudotuberculosis, etc., and to 
insure the fact that the toxine was not injected into the muscles or the 
peritoneum — Avhich may have rendered the animals more susceptible. 
The guinea pig shows a remarkable constancy in its reaction to A"aiy- 
ing amounts of the diphtheria poison. Overpowering doses of the 
toxine — say, lOOxMLD — almost iiiA^ariably kill the animals in about 
tAventy-four hours. It is with the rarest exception that a guinea pig 
will die as a result of the diphtheria poison in less than twenty hours. 
Smaller amounts cause the death of the animal in from thirty -six to 
forty-eight hours. As we approach the limit of the minimal lethal 
dose, or the mixture containing the L-j-dose of the toxine and one 
immunity unit, we find one of three results; 
(1) The animal dies from acute poisoning’ on about the fourth day. 
(2) The animal develops post-diphtheritic paralysis betAveen the four- 
teenth and thirtieth days. 
(3) RecoA"ery. 
