OF THE ALIMENTARY TRACT 181 



As with most of the intestinal protozoa the cyst 

 is the transmissible form. The trophozoite does not 

 appear in the natural stool and even when passed 

 from the intestine, as in diarrhoea, it is so delicate 

 that it does not live long and is apparently incapable 

 of surviving exposure to the acid of the stomach for 

 a sufficient period to allow it to pass alive to the duo- 

 denum. 



It has been observed in stomach contents when 

 there was no trace of free hydrochloric acid, but was 

 almost immediately destroyed by gastric juice of nor- 

 mal acidity and by 0.1% hydrochloric acid in 0.9% 

 sodium chloride solution. Although it is not impos- 

 sible that some of the other encysting protozoa of 

 man's intestine may pass in viable trophozoite form 

 through the stomach at times, Giardia intestinalis 

 apparently never does. 



EXAMINATION FOR GIARDIA 



The routine stool examination practice given un- 

 der the amoebae is sufficient for determining the pres- 

 ence of Giardia intestinalis when it is appearing in 

 stools. When there is diarrhoea it is usually present 

 in active form, and a late specimen following a saline 

 purgative will usually bring it out in this form. 

 Otherwise it is only the cysts which appear and they 

 irregularly or periodically, so that it is difficult to be 

 certain- that it is not present from even several ex- 

 aminations. In this case, except in liquid stool, it 



