107 



infection is proportional to the time exposed. The infection is, how- 

 ever, a variable quantity, and no definite statements can be deduced. 



As the lambs do not begin to nibble grass and drink water until some 

 few days after their birth, the development of tcenia in K and L prob- 

 ably required not over two months. Lamb A, examined October 21, 

 about twenty- three weeks after birth, gives, when compared with K 

 and L, an approximate rate of growth of the tcenia of 2"™ a montli, 

 more or less. The rate of growth must so vary at different times that 

 no definite rate can be determined at present. 



The twniai of No. 105, one of the same lot of lambs as the foregoing, 

 were no larger after thirty-two weeks than those of K and L after ten 

 weeks. This points to a recent infection of No. 105, i. e., within ten 

 weeks, or about the time the lambs were taken off the prairie and re- 

 ceived into the corral. The twniw of Nos. 107, 109, 108, and 106 coin- 

 cide with this ; but the lambs No. 109 and 108 also point to a later in- 

 fection, as many very small twnice were found in them. No. 108, which 

 had tcenia; 1"™ long six weeks after its receipt in Washington, would 

 lead us to suspect a recent infection ; but this is not necessarily the 

 case, as the influence of the rumen of the sheep in detaining the para- 

 site for a length of time has yet to be learned. The absence of young 

 tcenicB measuring less than 7"™ in No. 106 at sixteen weeks after its 

 last association with an animal containing adult tcvmice and twenty 

 weeks after its arrival in Washington is also of interest in that it points 

 to infection of the lamb from the adult sheep associated with it. No. 

 110 shows a very slight infection, and one, judging from the age of 

 tcenice, that could have occurred in Colorado. 



The six cases show a, slow growth of the parasite ; they also point to 

 one of two things: That the tcenice are, as embryos, retained in the 

 rumen for some time after being swallowed, or that these tcenicB are 

 continually infecting their hosts by the direct method ; that is, the 

 embryos passed by sheep, with little or no preparation, pass into other 

 sheep and develop without the intervention of an intermediary host. 

 So far nothing has been found to absolutely prove or disprove the latter 

 statement. The infection, as shown by the various sizes found in these 

 lambs and other sheep, points to a continuous infection nearly all the 

 year. (See Tables A, B, and 0.) 



Nos. 106 and 110 indicate a cessation of the infection for the length 

 of time it required the smallest (7<"") to attain their size. Lamb A in- 

 dicates the time to be something less than twenty weeks, or at the 

 period when they were received at Washington. Nos. 106, 107, 108, and 

 109, which had been confined eleven and twelve weeks, show as great 

 infection as has been seen. This would happen with animals which 

 were being infected iii confinement, for the opportunities of infection, 

 if the infection should prove to be direct, are greater. "Various condi- 

 tions, as the weather, food, water, etc., have so much to do with the 

 problem of infection that far more data are necessary. 



