53 SCIENCE PROGRESS 



the longer, for though the bones of both have been found 

 associated with the remains of prehistoric man, this may merely 

 indicate that they were used for food, and representations 

 of both animals are found upon the ancient Egyptian monuments. 

 Yet there can be little doubt that the cat is nearer the original 

 wild form than the dog. This is shown by its instincts and 

 habits. The cat, for instance, never exhibits the same devotion 

 to men that the dog does ; and, as Darwin points out, cats are 

 always eager to attack poultry, while dogs, even when quite 

 young, rarely show such a tendency. Further, the nocturnal 

 habits of the domesticated cat, and the survival of the wild 

 cat, enabled frequent crossings to occur long after such a process 

 became rare or impossible for dogs. 



Next comes a group comprising some of our familiar 

 domesticated cattle, viz. goats, pigs, cows, and calves. These 

 animals are only at times under adverse conditions. Whilst 

 in the fields they enjoy their natural environment. But when 

 they are shut up in stalls and byres they breathe a confined 

 and tainted atmosphere, they are brought in contact with man, 

 they risk catching his diseases. Under such circumstances 

 the struggle has been only moderately severe, and the sus- 

 ceptibility of these animals to tuberculosis accordingly remains 

 considerable. 



At the end of the list are rabbits, monkeys, apes, and guinea- 

 pigs, all wild forms, for the last, though now bred in captivity, 

 was not introduced into Europe from South America until the 

 sixteenth century. In their native forests and prairies these 

 animals have never felt the touch of civilisation. They have 

 never been subjected to any selection against tuberculosis, and, 

 consequently, in their totally unprotected state, the disease 

 attacks them with terrible virulence. 



One point more may be mentioned. When both adult 

 and young forms of the same species were examined, it was 

 invariably found that the latter displayed greater susceptibility 

 than the former. Thus calves were more susceptible than 

 cows, kittens than cats, and puppies than dogs. This again 

 agrees with what is found in the human species, for, with the 

 exception of pulmonary tuberculosis, all forms of the disease 

 are of much greater prevalence among children than among 

 adults ; and as regards such affections as measles and scarlet 

 fever, their enormously greater prevalence among the young 



