The Histogenesis of Cysticercus pisiformis. 185 



In the first two full grown rabbits were used with entirely 

 unsatisfactory results. One of these rabbits contained no traces of 

 immediate infection with Cysticercus pisiformis. The other 

 rabbit contained 11 well grown Cysticercus pisiformis, but since 

 the liver was healthy at the time of dissection it is highly probable 

 that these larvae were not the result of the experimental feeding. 



A second experiment performed on an adult cottontail rabbit 

 was equally unsuccessful. But experiments performed on 3'oung- 

 Belgian hares (Lepus cuniculus) and on a young Lepus pinetis were 

 in most cases productive of excellent results. 



These results however differed widely in different experiments, 

 conducted under the same conditions and with rabbits of the same 

 age and species. The reason for this must be supposed to lie in 

 the individuality of different rabbits. The failure of the first two 

 experiments may be attributed to the fact that they were performed 

 on full-grown rabbits, which are probably less open to infection 

 than young rabbits. Vogel (1888) believed that a previous infection 

 with C. fasciolaris rendered mice to a certain extent immune to 

 successive infection. In my own experiments, hoAvever, such an 

 hypothesis is open to grave doubt since I have found hundreds of 

 larvae of different ages in a single specimen. Hofmaîvn (1901) and 

 Baetels (1902) both found difficulty in infecting adult mice with 

 C. fasciolaris, but Hofmaxn sliowed that the age was a factor of 

 decided importance, young mice being more easily infected than old. 

 My experiments support this view^, but they further tend to show" 

 that, as just stated, the difference in constitution of different indi- 

 viduals is also an important factor.^) 



A careful study was made by means of sections of the following- 

 organs and tissues of two of the infected rabbits: ovary. Fallopian 

 tube, brain, spinal cord, sub-cutaneous connective tissue, voluntary 

 muscles, heart, thymus, lungs, large artery, portal vein, inferior vena 

 cava, pancreas, great omentum, liver, spleen, kidney, testis, gall 

 bladder, urinary bladder, stomach, small and large intestine; and 

 the following were found infected: liver, omentum, lungs, lymph 

 glands in the mesentery and pancreas. In the latter organ no larvae 



1) It is possible also that the age of the proglottids employed, and 

 the period intervening between the time at which tliey were voided by 

 the dog and that at which they were fed to the rabbit , may have had 

 an effect upon the results. 



13* 



