Doncaster Microscopical Society
Pork and its Parasites
The twelfth ordinary meeting of the above society was held on Wednesday evening the 18th inst. The Rev. W. H. Weston (vice-president) in the chair. Thirteen members were present.
In the absence of Mr. J. B. Witherington two papers were read on the Parasites Infesting Pork; one by Dr. J. Mitchell Wilson on Trichina Spiralis, the other by Mr. W. Walker on Cysticerous Cellulosa. As a large amount of interest throughout this and other countries has recently been manifested in the parasitical diseases affecting pork and which are capable of being communicated to man, the following points alluded to by Dr. Wilson and Mr. Walker may be of interest to general readers.
The Trichina Spiralis belongs to the group of round worms and is most frequently observed enclosed in a cell or cyst coiled up in spiral shape. These cysts which are formed only among the muscles of the meat are scarcely visible to the naked eye. Under the microscope the worm in its free state measures in the female one-eighth of an inch in length; in the male only one-eighteenth of an inch.
The young in each female have been estimated at from 10,000 to 15,000, within two or three weeks after obtaining an entrance into the stomach, say from imperfectly cooked pork; these enormous numbers of young trichina are born and at once begin their wanderings. They burrow along the muscular tissues becoming encysted, and it is during this stage that the violent muscular pains are experienced which are a prominent sign of the disease in man.
Dr. Cobbold estimated that in one person who had eaten a known quantity of pork infested with trichina there would be at least 42,000,000 parasites. Some of the epidemics which have occurred in Germany have caused a mortality of less than 2 per cent Of the persons attacked, while in 1885 an outbreak in one town attacked 350 persons of whom 100 died.
Numerous inquiries have been made as to the prevalence of this parasite in pork in different countries. In 1866 out of 1400 hogs examined at Chicago 28 were found infected or 1 in 50, the number of worms in each cubic inch varying from 48 to 18,000. In France the disease Trichiniasis has always been rare. In Germany the disease has been much reduced since the introduction of compulsory microscopical examination.
Professor Gamgee states that the Yorkshire and Berkshire pigs are generally free from worms. He adds, we disregard the most common precautions to protect ourselves against disease by allowing piggeries where all kinds of garbage charged with worms, or their eggs, are devoured by swine. Dr. Wilson had carefully examined 18 specimens of pork obtained from shops in different parts of his district, but in none of these were any trichina found.
Specimens were, however, shown obtained from a friend at a distance from a piece of ham infected with the parasite, and other prepared slides exhibited infected muscle both from man and the pig.
It is said that a temperature of 150o F. kills the free trichina, but the encapsuled worms are able to resist a greater degree of heat and are not destroyed by the usual methods, pickling and roasting the meat. If the interior of a piece of meat roasted or boiled retains much of the blood and colour of uncooked meat the temperature has not been higher than 130o F.
These facts ought to lead us to observe the advice of the Medical Officer to the Local Government Board, who says that any sample of meat thought to contain the parasite ought not on any account to be eaten, no matter how it is cooked, and that the only means of avoiding disease in man from the dangers arising from trichina in meat from pigs is by very thorough and efficient cooking, which means cooking it one half as much again as the ordinary rule.
At the conclusion of Dr, Wilson’s paper, Mr. Wm. Walker, M.R.C.S., gave a short account of cysticercus cellusosa, the larval form of the tapeworm, Toenia Solium.
The presence of this parasite constitutes that disease in the pig commonly known as the measles. Under the microscope they appear as small egg-shaped bodies lying between the muscular fibres. Although the larval are found in other animals besides pig, the mature tape-worm exists only in man. The head of the cysticercus is of globular form and furnished with four suckers round the margin and 14 or more hooklets in the centre. When the egg or germ of the tape-worm is swallowed by an animal it is hatched in the stomach and afterwards forces its way into the various tissues of the body, where, like the trichina, it becomes encapsulated and remains dormant, forming the cysticercus.
When flesh thus infected is swallowed by man the cysticercus develops into the fully formed tape-worm. In connection with this parasite there is the advantage that when present it cannot easily be overlooked as the meat infected with it has very characteristic appearance. Should there be any doubt the discovery of the hooklets under the microscope would at once dispel it.
The reading of the papers was followed by an interesting discussion in which the chairman, and authors, the Rev. W. Smith, and Messrs. Burman, Kirk, Stiles, and Tindall took part. The meeting terminated with a vote of thanks to Dr. J. Mitchell Wilson and Mr. Walker