STÜDY OF DELAYED OR « LATENT » TUBERCULOUS INFECTION 607 
capable of producing tuberculosis, but the mode of spread of 
tbe infection was anormal. In the subcutaneous tissue and 
subjacent muscles in the neighbourhood of the seat of inocu¬ 
lation on the inner aspect of the leg, a large number of small 
isolated or confluent tubercles formed during the first month, 
and it was only towards the end of the first month that the 
inguinal glands began to enlarge. When the cobayes were 
killed, 3 months after inoculation, it was found that the tissues 
on the inner aspect of the thigh and the abdominal walls, 
including the peritoneum, in the corresponding inguinal 
région were the seat ot a very large number of small fibro- 
caseous tubercles, almost confluent; the lymphatic glands 
behind the diaphragm were not more affected than is gene- 
rally found to be the case 3 or 4 weeks after inoculation, but 
the liver, spleen, the lungs and most of the lymphatics in front 
of the diaphragm were the seat of extensive tuberculous lésions. 
There appeared, therefore, to hâve heen during the first 
month a tendency to a localisation of the infeclive process, but 
afterwards the infective organisme which had been able to 
pass beyond the locality first affected, must hâve regained 
their virulence and power to mulliply, for the organs situated 
at a distance from the seat of inoculation showed lésions resem- 
hling closely those observed in the course of normal infection. 
Similar effects were observed in the case of tuberculous cul¬ 
tures and tuberculous milk which had been heated for a defi- 
nite length of time up to températures approaching léthal 
températures. 
While conducting in 1899 a sériés of experiments on the 
sterilization of milk artificially infected with luhercle bacilli of 
human and of bovine origin, the writer observed that cobayes 
inoculed with milk which had been submitted to certain tem¬ 
pératures for a certain length of time remained apparently free 
from infection for several weeks, but that ultimately they 
became tuberculous. This delayed infection was observed 
when the milk had been heated to : 
65° C. for 180 minutes (3 hours). 
70° C. — 45 — 
74° C. — 30 — 
76° C. — 10 — 
85°C. — 15 — (In this case there was a delay of 2 months). 
