MICROSCOPIC EXAMINATION OF EXCRETA. 147 



thrice as long as the others. Like the eggs of Distomum lanceolatum 

 and Bothriocephalus, they bear a small, usually inconspicuous, lid at 

 one end. The eggs of the two species of Tcenia are provided with an 

 extremely thick shell, the more conspicuous since it has a brown 

 colour and distinct radial markings, caused by a covering of closely 

 packed little rods. The eggs of Ascaris lumbricoides and Trichocephalus 

 dispar are also thick-shelled, and the former are further enveloped in 

 an albuminous sheath, usually coloured with bile pigment, while the 

 latter are perforated at the poles and provided with an albuminous plug. 

 The contents of the eggs also vary, being sometimes, indeed usually, 

 unaltered, but sometimes in process of yelk-division (Dochmius), or even 

 already exhibiting an embryo, as in Tcenia solum, T. saginata, and 

 Oxyuris. In the last instance the embryo is only partially developed. 

 We can to a certain extent infer the proportionate number of the 

 different parent parasites from the quantity of eggs expelled from the 

 host, but in so doing we must remember that the fertility of the 

 various forms is by no means equal. And further, the eggs will be 

 more easily and more abundantly found the nearer the parasite is to 

 the anus, for then they will not be indifferently mixed through the 

 faeces, but will be found especially in the outer portion and mucous 

 surroundings. The eggs of Oxyuris are most easily demonstrated. 

 This statement is consistent with the result of Vix, who among 

 his patients affected with Oxyuris never found a single case where 

 the eggs were not to be observed in countless numbers in the first 

 microscopic preparation, or even first field of vision. Vix recom- 

 mends further the examination not of the faeces, but only of the 

 mucus, which can be easily removed from the anus or higher portion 

 of the rectum with the handle of a scalpel or catheter. This method 

 might suffice for Oxyuris, but is less likely to succeed in the case 

 of other parasites which infest higher portions of the alimentary 

 canal, and whose eggs are chiefly found in the faeces themselves. 

 Therefore, in suspected cases of helminthiasis, the faeces ought not 

 to be left unexamined, even when the examination of the mucus yields 

 no positive result. 



We need not further discuss the methods of examination, since 

 these will partly suggest themselves in the course of what is certainly 

 not a very pleasant task. 



It ought, however, to be specially noted that in some established 

 cases of Tcenia the eggs are sought for in vain. This is readily in- 

 telligible when we remember what we have previously (p. 65) men- 

 tioned, that the eggs of these animals are not liberated within the 

 alimentary canal, but reach the exterior still enclosed in the proglottides. 

 The eggs which, in spite of this, are found here and there in the faeces, 



