8 
under examination, and in the work referred to 1 c. c. was sufficient 
to cause the death of pigs with a hypersusceptibility transmitted from 
the mother. 
Second. If treated and recovered pigs are used as breeders and their 
young prove more resistant to diphtheria toxine, then when tests of 
serum are made on such resistant pigs we would evidently obtain 
misleading results. 
Third. If these young pigs are of average susceptibility the recov- 
ered pigs could be used as breeders, resulting in quite a saving in 
animals bought for breeding purposes. 
The use of such used animals as breeders was the custom in two 
antitoxin laboratories that I personally know of. and I suggested it as 
one explanation of irregularities they encountered in the testing of 
antitoxin. Both eliminated these used animals from their breeding 
pens with a decided decrease in the number of irregular results. 
No pigs have been bought for use in the Hygienic Laboratory since 
May 31, 1905, the number raised being ample. We obtained pigs 
from three sources for breeding purposes, by far the larger number 
being presented to the laboratory by the Bureau of Animal Industry, 
none of which. I am sure, for many generations back had any taint of 
diphtheria toxine. As to the other two sources of supply I can not be 
so sure; but all of those received at the laboratory were under 300 
grams in weight and consequently would not have been used for work 
with diphtheria toxine. Since May, 1905, we have used 3,139 pigs for 
the testing of diphtheria toxine or antitoxin. During this time a care- 
ful search of the records shows a very small number of pigs which died 
much earlier than was to be expected with the dose given, and some of 
these presented pneumonia at the autopsy. Only three have failed to 
die acutely when used on the L4- dose, thus showing very plainly that 
marked resistance to diphtheria toxine is unusual in the pigs bred at 
the H} T gienic Laboratory. 
Theobald Smith , a in giving the results of tests of the young of three 
female pigs in which there was an immunity transmitted from the 
mother, sa} T s that this may be due to (1) the influence of any prelimi- 
naiy treatment, (2) the influence of the male, (3) the influence of selec- 
tion in breeding. He considers his data sufficient to rule out the first, 
but states that the mother of his most resistant pigs (No. 2911) had 
previously been treated with a toxine -antitoxin mixture and about 
four or five months afterwards put into the breeding pens. I think, 
in view of my results, that this treatment fully accounts for the 
immunity of her young. 
a Smith,. Theobald: Degrees of susceptibility to diphtheria toxin among guinea 
pigs; transmission from parents to offspring. Journ. med. research, vol. 13, n. s. vol. 
8, Feb., 1905, p. 341-348. 
