n 
sides of the s}^ringe, is in turn forced under the skin. Care to avoid 
the injection of an unnecessary 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, without 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 fluid 
escapes. We do not attempt to disinfect the skin. 
Effect upon the guinea pig . — After inoculation the guinea pigs are 
kept two in a cage and not disturbed until the seventh da}^ Keeping 
many animals together in a pen ma}’ give irregular results, because 
the strong and lusty pigs worry the sick ones and ma}^ hasten their 
end. Examining the pigs too often or too roughly must also be 
avoided. Theobald Smith believes that palpating the edema, caused 
b}" the reaction of the toxine at the site of inoculation, may cause the 
poison to break be^mnd the confines nature is setting up as a barrier, 
and ma}^ thus hasten the result. We have found that there is little to 
be learned in weighing or examining pigs during the first week, and 
we therefore leave them undisturbed during this time. The}" are 
weighed on the seventh day and each week following until the fourth 
week, when, if gaining weight and in good condition, they are passed 
from observation. 
Guinea pigs that show late effects of toxooie^ as indicated by paral- 
ysis, will do so some time after the fourteenth day and before the 
thirtieth day with great regularity. The facts of paralysis, sloughs, 
ulcers, etc., are carefully noted on the records. 
When an animal dies an autopsy is always 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 — which may have rendered the animals more susceptible. 
The guinea pig shoAvs a remarkable constancy in its reaction to vary- 
ing amounts of the diphtheria poison. OverpoAvering doses of the 
toxine — say, lOOxMLD — almost invariably kill the animals in about 
twenty-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 aa"o approach the limit of the minimal lethal 
dose, or the mixture containing the L-j-dose of the toxine and one 
immunity unit, Ave find one of three results: 
(1) The animal dies from acute poisoning on about the fourth day. 
(2) The animal deA'elops post-diphtheritic paralysis betAveen the four- 
teenth and thirtieth days. 
(3) RecoA"ery. 
