51 



probably often overlooked, and negative records cannot be re- 

 garded as reliable evidence of its absence. 



(6) Giardia intestinalis. — This flagellate — better known under 

 the name of Lamblia — occurs commonly in people who have 

 never left Britain. The first British infections were recorded by 

 Smith and Matthews (1916), and since then it has been found by 

 every worker who has examined cases of this class — including 

 Miss Mackinnon (1918) and Baylis (1919), in addition to those 

 whose work is here reported. 



The chief noteworthy fact about this protozoon is that it has 

 been found more frequently in children than in adults. The re- 

 corded figures are verj'^ striking, and may be briefly recapitulated 

 here : 



Percent. G. intesfincdis 



The uniformity with which Giardia has been found more 

 frequently in children cannot be accidental, and it seems clear 

 that these figures must have a real significance. But what this 

 significance is, is not so clear. Matthews and Smith (1919) in- 

 terpret their findings as indicating that infection with Giardia 

 is actually commoner in children than in adults. They believe 

 that this protozoon — and others found in the human bowel — 

 ' may disappear from the intestine in the course of time ' : ' it 

 may be that the flagellate is mainly a parasite of children and 

 becomes rarer in older people '. This may be true: but it must 

 be remembered that failure to find a given organism in the stools 

 is by no means the same thing as absence of it from the intestine. 

 It is often extremely difficult to detect Giardia infections — in 

 adults, at all events — by examination of the faeces ; and to find 

 an infection it may be necessary to prolong the examination until 

 the stools have been carefully searched on dozens of occasions.^ 

 Figures which I have elsewhere published * appear to indicate 

 that the chances are about 7 to 2 against the infection being de- 

 tected by means of a single examination of the stools of the 

 average infected individual. Further, neither Matthews and 

 Smith, nor any other workers, have yet been able to adduce 

 a single concrete case in which a Giardia infection has been 

 proved to have died out. This organism is, in my experience, 

 remarkably persistent. I have had one infected individual under 

 observation for over ten years ; and although it is frequently im- 

 possible to find the organism in the stools, the infection is still 



' These figures (adults) are for 1 ,098 Army recruits. 



' Percentages calculated by me from particulars entered on cards. 



' See my previous Report (1917), where this subject is considered at length. 



< Ibid. p. 18. 



