EFFECTS OF CHANGES IN THE DIET 107 



digestive tract. Dobell (1917), referring to infection in man, states 

 that "the expectation for the average infected case is that it will be 

 found positive twice in every five examinations." This method is, 

 however, time-consuming and, with such animals as rats, which 

 pass solid feces, is unreliable. Brug (1919) states that "cysts (of 

 amoebae in rats) may be found for several days in succession, then 

 for several days, weeks or months nothing may be found." This 

 difficulty with rats may be overcome by starving them for several 

 hours, then feeding bread tliat has been soaked in a saturated solu- 

 tion of magnesium sulphate (Kessel, 1923). Rats react to the 

 purgative-passing semi-liquid feces in about twelve hours. If the 

 animals are infected one can usually find abundant protozoa in 

 material passed after such treatment. Kessel claims to be able to 

 detect practically all cases of amoebic infections in rats after two 

 examinations by this method. 



Chiang (1925) advocates the use of a "high enema" of sodium 

 chloride solution as a substitute for examinations of rats by purga- 

 tive. He has employed this method in examinations for amoebae, 

 and claims it is just as effective as purging and much more rapid. 

 The method is as follows : A syringe is filled with 0.85% sodium 

 chloride solution and attached to a small rubber catheter which 

 is lubricated with oil or vaseline. The catheter is inserted ten 

 to fifteen centimeters into the rectum and five to ten cubic cen- 

 timeters of salt solution injected into the colon and cecum. The 

 rat retains the enema for several minutes. When passed it is col- 

 lected in a large Petri dish, and examined for protozoa. Ether 

 anesthesia may or may not be used, depending upon the tempera- 

 ment of the rat. 



These methods, though effective in determining the presence of 

 protozoa in the intestine of animals, are not suited for accurate 

 enumerations of the organisms actually living in the intestine. 

 They either depend upon finding organisms naturally passed in 

 the feces or carried out under abnormal conditions. Purgatives 

 may, under certain circumstances, entirely eliminate infections. 

 Kessel (1924) states that seven of nineteen control rats became 

 negative for amoebae following examination by the magnesium 

 sulphate method. Such an occurrence would no doubt lead to 

 erroneous interpretations of results if diets were being tested. 

 Hence these methods cannot be recommended. 



Surgical methods that enable one to remove a measured amount 



