1915] Kofoid and Cltristiaiiscii: On Giardia inuris (Gnissi) 



31 



auy event it has an important bearing on tlie extent and rate of 

 increase of the parasites and thus upon tlieir significance in human 

 and comparative medicine. 



It is the purpose of the present paper to describe binary and 

 nniltiple fission in both free and encysted Giardia, to describe mitosis 

 in the cells of this minute organism, to add to the scepticism regard- 

 ing autogamy and an Octomitus stage, and to bring some slight but 

 inconclusive evidence for maturation and conjugation. 



This paper is based on the examination of these parasites in gray 

 and white culture mice, field and meadow mice, rats, rabbits, and 

 coyotes which feed upon meadow mice, as tabulated below. In all 

 220 mammals were examined between August 26, 1914, and July 20, 

 1915. Of these, twenty-nine, or thirteen per cent, were obviously in- 

 fected with Giardia. It is possible that more complete examination 

 would have revealed them in some hosts in which they were not found. 

 Their seemingly entire absence in culture rats and in the rabbits 

 examined is noteworthy in view of the previous reports of the occur- 

 rence of Lamblia in these hosts. The absence in rats may be due to 

 the age of the hosts, most of those examined being old individuals. 

 Giardia is rare in old mice. 



Number Number 



Species e,\amined infected 



Culture mice 08 22 



Peromyscus maniculatus gambeli (Baird) .59 4 



MicroUis calif ornicus calif ornicus (Poale) 6 3 



Culture rats 42 



Belgian hares 12 



Canis ochropus ocJiropux Esehscholtz 2 



1 



1 



The distribution of infection by color, sex, and organ is indicated 

 below : 



Duodenum 



Oesopli- .Stom- and 



Host Brown White Male Female agus ach iejunui 



Culture mice 14 8 15 7 1 2 19 



Peromyscus 4 .... 3 10 2 



Microtus 3 .... 2 10 2 



tlium Caecum Colon Rectu 



21 14 15 12 



3 3 4 2 



3 2 1 



27 17 21 15 



The region of frequent and niaxiimun infection is the small intes- 

 tine in the duodenum and occasionally near the caecum, though both 

 above and below the latter it is often severe. Heavily infected ho.sts 



