52 



present, and has shown no signs of disappearing from the bowel. 

 The other common intestinal protozoa appear to be equally per- 

 sistent. 



I therefore hesitate to accept this obvious explanation. I be- 

 lieve the figures merely show that Giardia is more easily found 

 in the stools of children than in those of adults : they do not 

 prove that children as a whole are more frequently infected. On 

 the other hand, it appears quite probable that children, indi- 

 vidually, when infected have heavier infections than adult 

 individuals. This would not be surprising, and many analogous 

 instances in which young animals show, individually, a far higher 

 degj'ee of protozoal infection than adults of the same species 

 could easily be quoted. It seems not at all improbable that in 

 children, when recently infected, Giardia multiplies more rapidly, 

 and appears more copiously in the stools, than it does later in 

 adult individuals in whom the infection has become chronic. It 

 is perhaps easier, therefore, to find evidence of infection in 

 children ; but there is as yet no real evidence that children as 

 a class are more frequently infected than adults, and none that 

 Giardia infections tend to disappear when once established. 



There is some very interesting evidence to show the age at 

 which Giardia infections may be acquired. Matthews and Smith 

 (1919) found no intestinal protozoa in infants during the first 

 year of life : but they found several infections with Giardia — and 

 also with other protozoa— in children aged between one and two 

 years, and concluded that they ' may become infected with in- 

 testinal protozoa soon after they are twelve months old '. There 

 is conclusive evidence now, however, that Giardia infections at 

 least are contracted still earlier. . 



Miss Nutt, at Leeds and Sheffield, examined the stools of 

 25 children aged 12 months or less : and she found Giardia in 

 no less than 6 of these. Her results — compiled from her cards — 

 were as follows : 



These findings are, I think, very remarkable. That a child 

 only 3 weeks old may already harbour Giardia would hardly 

 have been suspected. It implies gross contamination of its food 

 with human faeces : and since all the intestinal protozoa are 

 transmitted by similar means, it shows that — where suitably dirty 

 conditions obtain — a child may become infected with any in- 

 testinal protozoon shortly after birth. 



(7) Chilomastix mesnili. — This flagellate appears to be fairly 

 common in Britain. It has been found by all the workers en- 

 gaged in the present investigation, but the incidence of infection 

 varies greatly in different records. Matthews and Smith (1919, 



