MICROSCOPIC OBJECTS. 58 



Fig. 115 . ENTOZOON. Trichina spiralis, from Human Muscle, 



x50. 



This Entozoon is particularly interesting, from the fact 

 that its presence in large numbers in pork renders the meat 

 diseased, and has produced in those who ate it an epidemic 

 called trichinosis. 



On the examination of the muscle in which the parasite 

 has taken up its abode, small specks will be seen (even with 

 the naked eye) ; and on placing the part under a moderate 

 power of the microscope, the worm will be seen coiled up in 

 its oval or circular orange- coloured cyst. The worms on 

 issuing from this cyst follow the course of the voluntary 

 muscles. Some of the worms die ; but even those that are 

 left often number 50,000 to a single ounce of flesh. 



The parasite is best when mounted in balsam. 



Fig. 116. A Wheel- animalcule (Squamella oblonga), x 100. 



The Rotatoria, or Wheel-animalcules, form a very inter- 

 esting class to all students of nature. Their chief character- 

 istics are rotatory or wheel-like organs, from which the genus 

 Rotifera and class Rotatoria derive their names. Tail-like 

 processes are present in most of the species, similar in shape 

 to the same appendage in the Cyclops (see fig. 119) ; and a 

 gizzard just below the mouth is to be seen in constant 

 motion, grinding &c., in nearly all the larger species. The 

 other parts of the alimentary canal, such as the stomach &c., 

 are short. The Rotatoria are found nearly everywhere where 

 the water is not putrid; they are very tenacious of life. 

 The most common species is Rotifer vulgaris ; this species 

 shows the ciliated wheels well. The Rotatoria are best seen 

 when examined in their natural state ; the above drawing is 

 taken directly from the living animal. 



They may be mounted in alcohol and water if great care is 

 taken ; but they are difficult to keep well. 



