44 GUIDE TO THE STUDY 



While free larval stages are readily obtained by teasing infected 

 muscle, an instructive demonstration is that of the action of the 

 digestive juices on the cysts. For this purpose pieces of infected 

 muscle the size of a pea are kept for a day or so at 38 to 40°C. in an 

 artificial gastric juice consisting of: scale pepsin (U.S. P.), 0.25 gram; 

 sodium chloride, 0.2 gram; hydrochloric acid (sp. gr. 1.19), 1 cc; water, 

 100. If an incubator is not available the experiment may be carried 

 out in a warm room. 



For maintaining a supply of trichina?, rabbits forcibly fed are prefer- 

 able to rats. They are more resistant to the infection and are often 

 more readily kept than are rats. 



CHARACTERISTICS OF THE TRICHUROIDEA 



To the superfamily Trichuroidea belong the famous trichina 

 worm and the whipworm of man, several important species affect- 

 ing the respiratory passages of carnivores, and a number of less 

 important forms. 



The group is characterized by the fact that the anterior 

 end of the long body is prolonged into a slender, more or less 

 whiplike portion, while the posterior end is more or less swollen 

 and contains the genital organs. The oesophagus is very long 

 and traverses a chain of large, single cells; there is no oesophageal 

 bulb, and the anus is terminal. The ovary is single and the 

 vulva is at the origin of the swollen part of the body. 



We shall use as a type the trichina worm, Trichinella spiralis. 



PRACTICAL WORK 



Encysted Larvae. — You will be furnished with a portion of 

 infected muscle or with prepared slides showing the larval or 

 cystic stages of trichina. If the former, snip with the scissors 

 very thin sections of the muscle, lengthwise of the fibers, and 

 mount under pressure between two slides held together by rubber 

 bands or by clips. Search for the lemon-shaped cysts showing 

 the coiled larvse. Can you find cysts containing more than a 

 single larva? More than two? It should be recalled that the 

 cyst is formed from connective tissue elements of the host and not 

 by the worms. If you have had the fresh material, supplement 

 your study by examination of prepared slides. Make drawings 

 illustrating the cysts and larvae and their relation to the muscle 

 tissue. 



Some months after the formation of cysts in a host, their 

 calcification sets in. This is the stage in which they were 

 early noted as gritty particles in the flesh of cadavers in the 



