SCIENCE AND INDUSTRY. 
The dog and cat fleas (Ctenocephalus canis and felis) are very often 
troublesome household pests, besides being frequently found on rats. 
Fleas usually leave rats as soon as they die, and, of course, seek 
some other source of food. 
Furthermore, human fleas bite rats, and fleas found on dogs and 
cats bite both human beings and rats. Again, as human fleas and 
fleas found on cats and dogs can live on rats as casual parasites, 
they are able, therefore, to play an important part in the transmissior 
of plague from rat to rat, or from rats to human beings, and vice versa. 
4. Trichinosis is a disease of man and animals caused by a parasite 
—small worm hardly visible to the naked eye—called the T'richina 
spiralis. 
Human beings acquire the disease by eating the flesh of infected 
pigs, and pigs become diseased through the agency of trichinous rats. 
The infected flesh contains larval Trichine spiralis, and when it is 
eaten by carnivorous animals the larve are set free from the muscle 
by the action of the digestive juices. When they reach the intestines 
they become adults and sexually mature. Hach female gives birth to 
a large number of embryos. Some of these are excreted in the feces, 
but most of them are carried to the muscles in the blood stream. The 
embryos, which invade the muscles, become coiled up and surrounded by 
a cyst wall formed by the tissues, and they remain alive in this situation: 
for a considerable time. Animals may be infected not only by eating 
the flesh of other infected animals, but also by consuming other food 
which has been soiled by faeces containing the larval forms. It will be 
readily understood, then, how pigs may infect cach other through their 
feces. It should be borne in mind, however, that probably the main 
factor ,in the upkeep of Trichina spiralis is the rat, for these animals 
are very easily infected, and are not infrequently, in nature, harborers 
of the parasite. Again, as they commonly exist about piggeries, they 
may soil the food of the pigs with their excretions while the parasites are 
in their intestines, or they may be eaten by pigs, and so give rise to 
disease in the latter animals. As an illustration of how human food 
may become contaminated with the active elements of this most repul- 
sive disease through the agency of rats, the following case will suffice :— 
In February, 1909, at Exeter, two persons who had consumed some 
salted pig’s flesh became seriously ill. One of them, a labourer, was 
thought by his medical attendant to be suffering from trichinosis. A 
specimen of the salted pig’s flesh was then sent to the Veterinary 
Department of the Board of Agriculture, where it was examined, and 
found badly infested with Trichina spiralis. On making inquiries at 
a farm, it was found that the flesh had come from a sow which had 
been ailing for about two weeks before it was slaughtered. Although the 
‘sow was in good condition and fed well, she had shown great difficulty 
in using her hind-quarters, so much so that she had even to be assisted 
to rise. On this account she was slaughtered, pickled, and used for 
food. On making further inquiries, the farm premises were found to 
be overrun by rats. One of these was secured, and upon examination 
its abdominal muscles were found to contain a very large number of 
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