2 Lazcllc B. Stnrdcvant 



ous solution of corrosive sublimate and 70 per cent alcohol with 

 a trace of glacial acetic acid. For catchuig the hosts of this worm 

 I have found the genuine Marty trap an absolute necessity. I 

 have, where possible, killed and examined the animals on the 

 same day that they were captured. 



This paper was prepared under the direction of Dr. Henry B. 

 Ward, to whom I here express my sincere thanks for innumerable 

 suggestions and valuable assisiance. I am indebted to Mr. I. J. 

 Clark for a portion of my collection data. 



DEGREE OF INFECTION OF RATS EXAMINED 



Of the 103 rats examined 2y (26 per cent) were free from in- 

 ternal macroscopic parasites. Of these 7 were infested with ecto- 

 parasites and 2 others harbored a trypanosome m the blood. 



The stomach was infected with nematodes in three cases ( 2.9 

 per cent) ; from one to six worms were present in each case with 

 an average of three. They were free in the contents of the stom- 

 ach in two cases, but attached to the wall in a third. In these 

 three rats from 7 to 100 cestodes were present in each case. Two 

 nematodes were found in the small intestine in one of these cases 

 and in this rat two acephalic cestodes were also found in the 

 stomach along with the nematodes mentioned above. This last 

 condition is to be explained by reversed peristalsis, since the ani- 

 mal was not examined until several hours after death, and serves 

 to emphasize the necessity of immediate examination. One of 

 these hosts harbored a cysticercus in the liver, while one con- 

 tained a cyst in that organ. Ectoparasites were found in one case 

 and trypanosomes in the blood of this same host. 



Including the three cases just discussed, 67 rats (65 per cent) 

 harbored a total of 1,695 cestodes by actual count, except in one 

 case where an estimation of 100 was made. The minimum in- 

 fection was I cestode, the maximum 137, the average 25. From 

 September to December inclusive the minimum percentage of 

 rats harboring cestodes was 62.5 in September, the maximum 

 67.8 in November. The average number of cestodes found in 

 each case varied from a minimum of 9 in September to 28 in No- 



136 



