COCCIDIOSIS IN BIRDS AND MAMMALS 295 



type of animal used. StoU (i923rt) found, dealing with hookworm 

 ova in human feces, that it was necessary to adjust counts made 

 on mushy or diarrheic stools to the basis of formed feces by mul- 

 tiplying the egg-count on mushy stools by two, and on diarrheic 

 stools by four. Herrick (1928) found that the variability in counts 

 of hookworm eggs in canine feces was fifty-one per cent greater 

 when the feces were classified as formed, mushy, and diarrheic 

 and adjustments are made on the basis of the 1:2:4 ratio than 

 when they are counted without regard to consistency. 



Ex cy station. It is possible to produce excystation of coccidial 

 oocysts in vitro or in vivo. The process has not been exhaustively 

 studied. The technique involved is useful not only as a means of 

 inquiring into the nature of the process per sc but should be a 

 valuable adjunct in the study of the mechanism of host-parasite 

 specificity, as a means of determining the viability of oocysts, and 

 will perhaps assist in other similar procedures. 



In vitro excystation has been best described by Krijgsman 

 (1926). His paper contains a fairly complete review of the litera- 

 ture on the subject. He uses the washed concentrated oocysts from 

 the feces of the rabbit. After these have been centrifuged in dis- 

 tilled water, the water is replaced by a solution of pepsin in 0.5 

 per cent hydrochloric acid. They are exposed to the action of this 

 enzyme for thirty minutes, after which they are washed by cen- 

 trifuging in two changes of distilled water. The sediment contain- 

 ing the oocysts is suspended in a hanging drop of trypsin in 

 slightly alkaline solution. Excystation commences within two hours. 

 Preliminary experiments showed that while excystation may be 

 produced by simple immersion in the pancreatic enzyme, the time 

 required is eight hours or over. Exposure to gastric enzymes did 

 not result in excystation but produced certam physical changes 

 in the cyst wall which were undoubtedly the efifect of the acid. 

 Thus excystation of coccidial oocysts, according to Krijgsman is 

 a process analogous to protein digestion — with gastric enzymes 

 playing a predigesting role, and pancreatic enzymes completing the 

 liberation of the sporozoites. 



Excystation in vivo has been repeatedly carried out by the author, 

 using the following simple technique (Andrews, 1930). Appar- 

 ently any species of coccidia in birds and mammals can be used. 

 Coccidia from cat, dog, guinea-pig, rabbit, pig, and prairie-dog 

 liave excysted with equal success. Young rats (75 to 100 grams) 



