F. WARE AND M. K. SRINIVASAN 293
judging from the final tuberculin and Johnin tests carried out in April 1940
the disease had failed to extend.
In April 1940, 33 animals, other than
very young calves, were available for test, viz. 2 cows from Bihar, 6 animals
from Assam, 4 cows from Mukteswar Dairy and 21 animals born in the herd
of which 12 had been vaccinated. The only ones to react were the vaccinated
animals. Following this test 6 animals (Nos. 67—70, 76 and 88), taken at
random from the non-reacting group, were slaughtered and a careful examina-
tion of the intestine by microscopical and cultural methods failed to show
any evidence of Johne's disease.
In seeking to explain the facts, two questions for consideration are the
susceptibility of breeds of Indian cattle and the possibility of infected animals
recovering under certain conditions. There is no record of experiments having
been carried out on the susceptibility of Indian cattle to Johne's disease, but
the disease has been reported from a number of provinces and it may be pre-
sumed that as with other cattle susceptibility is greatest in early life. M'Fad-
yean and Sheather [1916] for instance found that many individuals of the
bovine species offer a marked resistance to infection with Johne's disease,
that calves under 6 months take the infection more readily and that by 6
months of age calves are already becoming more resistant.
With regard to the second question, it is still uncertain whether complete
recovery—in the sense of destruction within the body of all Johne's bacilli—
occurs, but it is well known that apparent recovery, i.e. recovery in the clini¬
cal sense, occurs quite commonly when the environment (housing, feeding,
climatic factors) is favourable. Thus, months or even years may elapse
before symptoms appear in Johnin-reactors, while in infected European cattle
after the age of 5 years there develops an immunity which in some animals
is strong enough to prevent any marked decline in condition for a number of
years.
Hagan and Zeissig [1933] record the remarkable instance of a cow, experi-
mentally infected by feeding, which showed severe symptoms of Johne's
disease and was in fact judged to be at the point of death but which improved
and gradually reached normal condition, at the same time becoming a non-
reactor to avian tuberculin, though still continuing to react to the comple-
ment fixation test. At autopsy, however, it was found that infection had
not been eliminated since lesions and the characteristic bacilli were present
in the ileum and ileo-caecal valve. It is perhaps not unreasonable to think
that this animal might have recovered completely had she been allowed to
live long enough. And if an occasional advanced case of the disease may
recover, it is not unlikely that animals exposed to natural infection may
often contract the disease and recover without reaching the advanced stage
in which symptoms are produced.
That apparent recovery may take place in Indian cattle is suggested by
Cooper and Srinivasan [1931] who observed that a number of cattle sent from
Bihar to Mukteswar as suspected cases of Johne's disease owing to poor condi-
tion, diarrhoea and reaction to avian tuberculin, improved greatly when
subjected to good housing and liberal feeding. Within 2 months all diarrhoea
had stopped and it was then very difficult to realize that they were still in-
fected with Johne's disease. Whether these were examples of true recovery